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Carriage of resistant pneumococci by children in southern Israel and impact of conjugate vaccines on carriage

1999; Elsevier BV; Volume: 5; Linguagem: Inglês

10.1111/j.1469-0691.1999.tb00854.x

1469-0691

Ron Dagan, Drora Fraser, Noga Givon‐Lavi, Pablo Yagupsky,

Respiratory viral infections research

Streptococcus pneumoniae is an important cause of morbidity and mortality worldwide [1Robbins JB Austrian R Lee CJ et al.Considerations for formulating the second‐generation pneumococcal capsular polysaccharide vaccine with emphasis on the cross‐reactive types within groups.J Infect Dis. 1983; 148: 1136-1159Crossref PubMed Scopus (433) Google Scholar]. Its main reservoir is the nasopharynx. From the nasopharynx, the organism can: (1) enter the bloodstream to cause invasive infections such as sepsis, meningitis and infections in remote foci such as arthritis, osteomyelitis and cellulitis; (2) spread to adjacent mucosal tissues to cause mucosal infections such as otitis, sinusitis and pneumonia; and (3) be transmitted by direct contact and through aerosols to other individuals. Many individuals in a population are colonized with S. pneumoniae at any given time, and most children are colonized at some point during the first years of life [2Gray BM Turner ME Dillon Jr., HC Epidemiologic studies of Streptococcus pneumoniae in infants: the effects of season and age on pneumococcal acquisition and carriage in the first 24 months of life.Am J Epidemiol. 1982; 116: 692-703PubMed Google Scholar, 3Musher DM Infections caused by Streptococcus pneumoniae: clinical spectrum, pathogenesis, immunity and treatment.Clin Infect Dis. 1992; 14: 801-809Crossref PubMed Scopus (444) Google Scholar, 4Hendley JO Sande MA Stewart PM Gwaltney JM Spread of Streptococcus pneumoniae in families: carriage rates and distribution of types.J Infect Dis. 1975; 132: 55-61Crossref PubMed Scopus (210) Google Scholar]. Resistance of pneumococci to antimicrobial agents, which was first reported in the mid-1960s [5Kisiak JW Razavi LM Daly AK Finland M Susceptibility of pneumococci to nine antibiotics.Am J Med Sci. 1965; 250: 261-268Crossref PubMed Scopus (134) Google Scholar, 6Hansman D Bullen M A resistant pneumococcus.Lancet. 1967; 2: 264-265Abstract Google Scholar], is increasing worldwide and has an enormous impact on clinicians, microbiologists, drug manufacturers, and public-health authorities [7Munford RS Murphy TV Antimicrobial resistance in Streptococcus pneumoniae: can immunization prevent its spread.J Invest Med. 1994; 42: 613-621PubMed Google Scholar, 8Friediand IR McCracken Jr., GH Management of infections caused by antibiotic‐resistant Streptococcus pneumoniae.N Engl J Med. 1994; 331: 377-382Crossref PubMed Scopus (558) Google Scholar, 9Appelbaum PC Antimicrobial resistance in Streptococcus pneumoniae: an overview.Clin Infect Dis. 1992; 15: 77-83Crossref PubMed Scopus (837) Google Scholar, 10Tomasz A The pneumococcus at the gates.N Engl J Med. 1995; 333: 514-515Crossref PubMed Scopus (70) Google Scholar]. Antibiotic-resistant pneumococci are more often carried by infants and young children than by adults [11Koornhof HJ Wasas A Klugman K Antimicrobial resistance in Streptococcus pneumoniae: a South African perspective.Clin Infect Dis J. 1992; 15: 84-94Crossref PubMed Scopus (157) Google Scholar, 12Radetsky MS Johansen T Lauer B et al.Multiply resistant pneumococcus causing meningitis: its epidemiology within a day‐care centre.Lancet. 1981; 2: 771-773Abstract PubMed Scopus (132) Google Scholar, 13Reichler MR Allphin AA Breiman RF et al.The spread of multiply resistant Streptococcus pneumoniae at a day care center in Ohio.J Infect Dis. 1992; 166: 1346-1353Crossref PubMed Scopus (344) Google Scholar]. Furthermore, since most of the resistant strains belong to only a limited number of serotypes, which are also among the most common causes of pediatric infections [7Munford RS Murphy TV Antimicrobial resistance in Streptococcus pneumoniae: can immunization prevent its spread.J Invest Med. 1994; 42: 613-621PubMed Google Scholar, 14Dagan R Yagupsky P Goldbart A Wasas A Klugman K Increasing prevalence of penicillin‐resistant pneumococcal infections in children in southern Israel: implications for future immunization policies.Pediatr Infect Dis J. 1994; 13: 782-786Crossref PubMed Scopus (78) Google Scholar, 15Breiman R Butler J Tenover F Elliott J Facklam R Emergence of drug‐resistant pneumococcal infections in the United States.JAMA. 1994; 271: 1831-1835Crossref PubMed Scopus (559) Google Scholar, 16Haglund LA Istre GR Pickett DA Welch DF Fine DP the Pneumococcus Study Group Invasive pneumococcal disease in central Oklahoma: emergence of high‐level penicillin resistance and multiple antibiotic resistance.).Infect Dis. 1993; 168: 1532-1536Crossref Scopus (54) Google Scholar, 17Welby P Keller P Cromien J Tebas P Scorch G Resistance to penicillin and non‐beta‐lactam antibiotics of Streptococcus pneumoniae at a children's hospital.Pediatr Infect Dis J. 1994; 13: 281-287Crossref PubMed Scopus (80) Google Scholar], conjugate vaccines aimed at these antigens may provide a useful tool to reduce nasopharyngeal carriage and limit the spread of resistant pneumococci. The goal of this communication is to describe the carriage of antibiotic-resistant S. pneumoniae in children in southern Israel and to review the current experience of the effect of the new conjugate pneumococcal Vaccines on carriage of S. pneumoniae in general, and that of antibiotic-resistant S. pneumoniae in particular, from studies in our region. The Negev region in southern Israel constitutes 60% of the land mass of the country while having less than 8% of the population. The area is largely desert, with high daytime temperatures, especially in the summer months, and low night-time temperatures, especially in the winter. There are about 20 days of rain annually. The two major population subgroups living in the area are Jews, largely concentrated in urban areas, and Bedouin Arabs, who are in transition from their traditional nomadic ways to a semi-urban westernized lifestyle. While the Jewish population (over 77% of the population) resembles that of the rest of Israel in sociocultural and ethnic characteristics, except for the slightly lower overall socio-economic level, the Bedouins form a unique population group. They retain their traditions in certain aspects of their lives, including polygamy (up to four wives are allowed by Islamic law). This population has an extremely high birth rate. The high birth rate, low socio-economic status, overcrowding, bad housing conditions and poor hygienic conditions result in high rates of infectious diseases, including respiratory illness, gastroenteritis and parasitic infections. The morbidity and birth rate patterns among the Jewish population are similar to those of the developed nations. In contrast, the Bedouins have the lifestyle and morbidity and mortality patterns of developing populations, while modern diagnostic and health care delivery services are all near at hand. We studied the carriage of S. pneumoniae in healthy children during the first 2 years of life seen at maternal child health centers during vaccination visits in the city of Beer-Sheva in southern Israel [18Dagan R Melamed R Muallem M Piglansky L Yagupsky P Nasopharyngeal colonization with antibiotic‐resistant pneumococci during the first two years of life in southern Israel: relation to serotypes likely to be included in the pneumococcal conjugate vaccines.J Infect Dis. 1996; 174: 1352-1355Crossref PubMed Scopus (146) Google Scholar]. We were struck by the high prevalence of carriage of S. pneumoniae in general, and the carriage of resistant S. pneumoniae in particular, among these healthy children (Figure 1). Approximately one-quarter of the children carried S. pneumoniae at 2 months of age, the rate increasing gradually to almost two-thirds at age 24 months. More alarming was the carriage of resistant S. pneumoniae among these healthy children: 11% and 27% carried S. pneumoniae resistant to at least one antibiotic drug at ages 2 and 24 months, respectively, and 4% and 18%, respectively, carried S. pneumoniae resistant to ≤2 drugs. Several important risk factors for the carriage of resistant S. pneumoniae were identified. They included recent antibiotic use (relative risk (RR) 2.6; confidence interval (CI) 1.9–3.5); the presence of older siblings at home (RR for penicillin-resistant S. pneumoniae 4.3; CI 1.0–18.1); and day-care attendance (RR 2.5; CI 2.2–2.9). It became obvious that not only was the day-care attendance important in itself, but also that the carriage of S. pneumoniae in general and resistant S. pneumoniae in particular was associated with the size of the day-care center as measured by the number of children in the group (Figure 2). The observation that factors such as the presence of siblings and day-care attendance pose a risk for carriage of S. pneumoniae implies that crowding is an important factor which facilitates the spread of S. pneumoniae. We therefore compared the carriage among Jewish children initially studied [18Dagan R Melamed R Muallem M Piglansky L Yagupsky P Nasopharyngeal colonization with antibiotic‐resistant pneumococci during the first two years of life in southern Israel: relation to serotypes likely to be included in the pneumococcal conjugate vaccines.J Infect Dis. 1996; 174: 1352-1355Crossref PubMed Scopus (146) Google Scholar] with the carriage among the Moslem Bedouin children in the region. This population is characterized by a high birth rate and overcrowding. In southern Israel, the crude birth rates in 1996 were 19.0/1000 and 55.9/1000 in Jews and Bedouins respectively. In addition, in Israel as a whole, only 4.3% of Jewish households had seven or more persons, while in the Moslem population 24.1% of households were overcrowded. As the birth rate of Negev Moslems is higher than that of the whole Moslem population of Israel (55.9/1000 and 37.2/1000 respectively), there is no doubt that the overcrowding rate in southern Israel is also higher [19Central Bureau of Statistics Statistical Abstracts of Israel, 1997. Vol. 48. Hemed Press Ltd, Jerusalem1997Google Scholar]. The nasopharyngeal carriage of S. pneumoniae among Bedouins was found to be 61%, 75% and 73% at ages 2, 6 and 12 months, respectively, compared with 26%, 39% and 38%, respectively, among the Jews (unpublished data). This higher carriage rate correlated with a 4.5-fold (P<0.0001) higher rate of invasive infections among the Bedouins than in the Jews [20Fraser D, Yagupsky P, Dagan R. A decade of pediatric invasive pneumococcal disease (IPD) in two populations residing in Israel: implications for vaccine choice. In: Pneumococcal Vaccines for the World, October, Washington DC, 1998; 26.Google Scholar]. To better characterize the spread of antibiotic-resistant S. pneumoniae in the day-care setting, we first studied the carriage in a day-care facility located in the city of Beer-Sheva, where nasopharyngeal cultures from S. pneumoniae were obtained every 2 weeks during a 10-month period [21Yagupsky P Porat N Fraser D et al.Acquisition, carriage, and transmission of pneumococci with decreased antibiotic susceptibility in young children attending a day care facility in southern Israel.J Infect Dis. 1998; 177: 1003-1012Crossref PubMed Scopus (145) Google Scholar]. Among the 48 children attending the day-care facility, S. pneumoniae was recovered in 362 of 573 (63%) of all cultures, and 60% of these isolates showed decreased susceptibility to ≤1 antibiotic drugs. By molecular methods we showed an extensive clonal spread involving several clones. Clones exhibiting decreased antibiotic susceptibility were more frequently isolated and persisted longer than did fully susceptible clones. This points towards a biological advantage for antibiotic-resistant pneumococci in a 'hostile' environment where multiple antibiotic use occurs frequently. We recently have studied children during the second and third year of life attending eight day-care centers, each located in a different neighborhood in the city of Beer-Sheva, all within a 5-mile diameter [22Givon N Fraser D Porat N Dagan R Day care centers as a site for development and amplification of Streptococcus pneumoniae nasopharyngeal carriage [abstract 305].Am J Epidemiol. 1998; 147: S77Google Scholar]. The distribution of serotypes and antibiotic susceptibility differed significantly between day-care centers. Furthermore, even when the same serotype with identical antibiotic susceptibility patterns was found in various day-care centers, ribotype restriction showed homogeneity within day-care center, but variability between day-care centers. These findings emphasize the important role played by day-care facilities in the transmission and augmentation of nasopharyngeal carriage of resistant S. pneumoniae in the community. They also emphasize that it is extremely difficult to make any generalization on the prevalence of serotypes or resistance from isolated studies. It is established that acquisition and carriage of S. pneumoniae is associated with the occurrence of acute otitis media [23Faden H Duffy L Wasielewski R et al.Relationship between nasopharyngeal colonization and the development of otitis media in children.J Infect Dis. 1997; 175: 1440-1445Crossref PubMed Scopus (404) Google Scholar], bacteremia [24Mastro TD Ghafoor A Nomani NK et al.Antimicrobial resistance of pneumococci in children with acute lower respiratory tract infection in Pakistan.Lancet. 1991; 337: 156-159Abstract PubMed Scopus (115) Google Scholar, 25Lehmann D Gratten M Montgomery J Susceptibility of pneumococcal carriage isolates to penicillin provides a conservative estimate of susceptibility of invasive pneumococci.Pediatr Infect Dis J. 1997; 16: 297-305Crossref PubMed Scopus (59) Google Scholar, 26Lloyd‐Evans N O'Dempsey TJD Baldeh I et al.Nasopharyngeal carriage of pneumococci in Gambian children and in their families.Pediatr Infecc Dis J. 1996; 15: 866-871Crossref PubMed Scopus (109) Google Scholar, 27Gray BM Converse III, GM Dillon Jr., HC Epidemiologic studies of Streptococcus pneumoniae in infants, acquisition, carriage and infection during the first 24 months of life.J Infect Dis. 1980; 142: 923-933Crossref PubMed Scopus (665) Google Scholar] and pneumonia [28Hodges RG Macleod CM Bernhard WG Epidemic pneumococcal pneumonia: III. Pneumococcal carrier studies.Am J Hyg. 1946; 44: 207-230PubMed Google Scholar], but is the high rate of carriage of resistant S. pneumoniae associated with identical rates of disease caused by resistant S. pneumoniae? It is certainly difficult to answer this question directly. However, much indirect evidence exists, at least in the case of acute otitis media. One way to answer this question indirectly is to examine the correlation between S. pneumoniae strains isolated from middle ear fluid in acute otitis media and those isolated at the same time from the nasopharynx. We have recently studied 112 pairs of isolates from middle ear fluid and nasopharynx obtained simultaneously from patients with acute otitis media (unpublished data). The main serotypes were 6B, 9V, 14, 18C, 19F, 19A and 23F, constituting together approximately 70% of all isolates. Of the 112 middle ear fluid isolates, 53% were penicillin susceptible and 47% were penicillin non-susceptible. In 90% of the cases, identical serotypes were isolated from both samples, and in 93%, identical susceptibility patterns were observed. Another way to examine the predictability of susceptibility of causative agents of acute otitis media by the patterns of nasopharyngeal isolates is to compare the patterns between nasopharyngeal isolates in healthy children and those isolated from middle ear fluid in children with acute otitis media. We have been studying this issue in an ongoing research project conducted in Beer-Sheva. The results of our interim analysis are shown in Figure 3. The nasopharyngeal isolates were obtained from healthy children attending maternal children health centers for vaccination and day-care centers, and the middle ear fluid isolates were obtained from children from the same area with acute otitis media visiting pediatric clinics and the Pediatric Emergency Room at the Soroka University Medical Center. Resistance in general and penicillin resistance in particular peaked at age 12–17 months, but was frequent among S. pneumoniae isolates in all ages. A clear correlation in percentage of penicillin-resistant isolates and resistance to ≤1 antibiotic drugs was found in the nasopharyngeal isolates from healthy children and those from middle ear fluid from children with acute otitis media. The somewhat higher resistance rate among the middle ear fluid isolates is most probably due to the more frequent selection of treatment failures among the patients in whom tympanocentesis is performed. We can therefore conclude that, at least for acute otitis media, which is the most common reason for antibiotic prescription in children [29Dagan R Can the choice of antibiotics for therapy of acute otitis media be logical.Eur J Clin Microbiol Infect Dis. 1998; 17: 1-5Crossref PubMed Scopus (24) Google Scholar], carriage of resistant S. pneumoniae in the community correlates with disease. This is important because of the strong correlation between the presence of antibiotic resistance among S. pneumoniae causing acute otitis media and the clinical and bacteriologic outcome [29Dagan R Can the choice of antibiotics for therapy of acute otitis media be logical.Eur J Clin Microbiol Infect Dis. 1998; 17: 1-5Crossref PubMed Scopus (24) Google Scholar, 30Leibovitz E Raiz S Piglansky L et al.Resistance pattern of middle car fluid isolates in acute otitis media recently treated with antibiotics.Pediatr Infect Dis J. 1998; 17: 463-469Crossref PubMed Scopus (98) Google Scholar, 31Dagan R Leibovitz E Greenberg D Yagupsky P Fliss DM Leiberman A Early eradication of pathogens from middle ear fluid during antibiotic treatment of acute otitis media is associated with improved clinical outcome.Pediatr Infect Dis J. 1998; 17: 776-782Crossref PubMed Scopus (142) Google Scholar]. Therefore, children nowadays find themselves in a dangerous vicious cycle: environmental factors associated with frequent and close contacts, such as the presence of siblings, crowding and day-care attendance, increase the frequency of both acute otitis media episodes and antibiotic resistance. High prevalence of antibiotic resistance decreases the frequency of successful treatment, which increases the frequency of antibiotic use, which in its turn selects for antibiotic resistance. To prevent this 'snowball' effect, it seems reasonable to examine the effect of pneumococcal vaccine on the carriage and transmission of pneumococci in general, and that of antibiotic-resistant pneumococci in particular [7Munford RS Murphy TV Antimicrobial resistance in Streptococcus pneumoniae: can immunization prevent its spread.J Invest Med. 1994; 42: 613-621PubMed Google Scholar, 32Austrian R Confronting drug‐resistant pneumococci.Ann Intern Med. 1994; 121: 807-809Crossref PubMed Scopus (60) Google Scholar, 33Klein DL Pneumococcal conjugate vaccines. Review and update.Microb Drug Resist. 1995; 1: 48-59Crossref Scopus (48) Google Scholar]. The new developments in conjugate pneumococcal vaccines are presented elsewhere in this supplement [34Klein D Eskola J Development and testing of Streptococcus pneumoniae conjugate vaccines.Clin Microbiol Infect. 1999; 5: S16-S28Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar]. Table 1 summarizes the most frequent pneumococcal serotypes/serogroups associated with the various types of disease worldwide. Serotypes/groups 6, 9, 14, 18, 19 and 23 are the most frequently found serotypes in invasive diseases, mucosal infections and carriage (with the exception of types 1 and 5, which are frequently isolated in invasive disease in the developing world, but are rarely found in mucosal infection and are carried even more rarely even in endemic areas).Table 1The most common worldwide pneumococcal serotypes/groups associated with diseases and carriageSerotype/group156914181923Nasopharyngeal carriage++++++Otitis media++++++InvasiveDeveloped world++++++Developing world++++++++Resistant S. pneumoniae++++++ Open table in a new tab The worldwide finding that most resistance is found among the serotypes most likely to cause disease in children [14Dagan R Yagupsky P Goldbart A Wasas A Klugman K Increasing prevalence of penicillin‐resistant pneumococcal infections in children in southern Israel: implications for future immunization policies.Pediatr Infect Dis J. 1994; 13: 782-786Crossref PubMed Scopus (78) Google Scholar, 15Breiman R Butler J Tenover F Elliott J Facklam R Emergence of drug‐resistant pneumococcal infections in the United States.JAMA. 1994; 271: 1831-1835Crossref PubMed Scopus (559) Google Scholar, 16Haglund LA Istre GR Pickett DA Welch DF Fine DP the Pneumococcus Study Group Invasive pneumococcal disease in central Oklahoma: emergence of high‐level penicillin resistance and multiple antibiotic resistance.).Infect Dis. 1993; 168: 1532-1536Crossref Scopus (54) Google Scholar, 17Welby P Keller P Cromien J Tebas P Scorch G Resistance to penicillin and non‐beta‐lactam antibiotics of Streptococcus pneumoniae at a children's hospital.Pediatr Infect Dis J. 1994; 13: 281-287Crossref PubMed Scopus (80) Google Scholar] is important. It suggests that if the newly developed vaccines are efficacious in reducing carriage of resistant S. pneumoniae, as was observed previously with the conjugate Haemophilus influenzae type b vaccines [35Mohle‐Boetani JC Ajello G Breneman E et al.Carriage of Haemophilus influenzae type b in children after widespread vaccination with conjugate Haemophilus influenzae type b vaccines.Pediatr Infect Dis J. 1993; 12: 589-593Crossref PubMed Scopus (136) Google Scholar, 36Murphy TV Pastor P Medley F Osterholm MT Granoff DM Decreased Haemophilus colonization in children vaccinated with Haemophilus influenzae type b conjugate vaccine.J Pediatr. 1993; 122: 517-523Abstract Full Text PDF PubMed Scopus (174) Google Scholar, 37Takala AK Santosham M Almeido‐Hill J et al.Vaccination with Haemophilus influenzae type b meningococcal protein conjugate vaccine reduces oropharyngeal carriage of Haemophilus influenzae type b among American Indian children.Pediatr Infect Dis J. 1993; 12: 593-599Crossref PubMed Scopus (98) Google Scholar, 38Takala AK Eskola J Leinonen M et al.Reduction in oropharyngeal carriage of Haemophilus influenzae type b (Hib) in children immunized with an Hib conjugate vaccine.J Infect Dis. 1991; 164: 982-986Crossref PubMed Scopus (347) Google Scholar, 39Barbour ML Mayon‐White RT Crook DW Coles C Moxon ER The influence of Haemophilus influenzae type b conjugate vaccine (PRP‐T) on oropharyngeal carriage of Haemophilus influenzae type b in infants under 12 months of age [abstract 304].in: Abstracts of the 33rd Interscience Conference on Antimicrobial Agents and Chemotherapy. New Orleans, LA. American Society for Microbiology, Washington DC1993: 175Google Scholar], the approach of reduction of spread of resistant organisms by immunization might be feasible, at least in part. The first report to show that conjugate pneumococcal vaccines might reduce the carriage of S. pneumoniae in general and that of resistant S. pneumoniae in particular was published by our group in 1996 [40Dagan R Melamed R Muallem M et al.Reduction of nasopharyngeal carriage of pneumococci during the second year of life by a heptavalent conjugate pneumococcal vaccine.J Infect Dis. 1996; 174: 1271-1278Crossref PubMed Scopus (400) Google Scholar]. In this study, we examined the effect of a seven-valent pneumococcal conjugate vaccine (which included serotypes 4, 6B, 9V, 14, 18C, 19F and 23F, conjugated to the outer-membrane protein complex of Neisseria meningitis group B; Pnc-OMPC) on carriage of S. pneumoniae and resistant S. pneumoniae of the serotypes included in the vaccine. Children aged 12–18 months were randomized to receive one dose of a conjugate heptavalent pneumococcal vaccine, two doses of the same vaccine, or one dose of a 23-valent native polysaccharide vaccine. Before immunization, pneumococcal serotypes included in the conjugate vaccine were isolated from 24% of the children, and an antibiotic-resistant pneumococcus was isolated from 22% of the children. The vaccines had no effect on carriage of non-vaccine-type pneumococci. In contrast, there was a significant reduction in carriage of vaccine-type pneumococci 3 months after one dose and 1 month after a second dose of conjugate vaccine (from 25% to 9% and 7%, respectively; P<0.001). No effect was seen after vaccination with the non-conjugate vaccine. One year after immunization, carriage of antibiotic-resistant vaccine-type pneumococci in children receiving conjugate vaccine was still lower than that in children receiving the non-conjugate vaccine (4% versus 14%, P = 0.042) (Figure 4). Shortly after this report, a second report was published by our group. This time, the effects of tetravalent (serotypes 6B, 14, 19F and 23F) vaccine in which the polysaccharides were conjugated to diphtheria toxoid (Pnc-D) or tetanus toxoid (Pnc-T) were compared to the effect of placebo when administered to infants in a randomized double-blind study [41Dagan R Muallem M Melamed R Leroy O Yagupsky P Reduction of pneumococcal nasopharyngeal carriage in early infancy after immunization with tetravalent pneumococcal vaccines conjugated to either tetanus toxoid or diphtheria toxoid.Pediatr Infect Dis J. 1997; 16: 1060-1064Crossref PubMed Scopus (197) Google Scholar]. The vaccines (or placebo) were injected at 2, 4 and 6 months of age. At 12 months of age, a native (non-conjugate) polysaccharide vaccine was administered as a booster. Nasopharyngeal cultures were obtained at 2, 4, 6, 7, 12 and 13 months of age. In general, carriage of all pneumococci (vaccine- and non-vaccine-related) was low at age 2 months and increased with age. However, for the vaccine-related serotypes (6A, 6B, 14, 19F and 23F), carriage was not increased with age in Pnc-D or Pnc-T recipients (Figure 5). Of all cultures obtained after the full primary series, seven of 72 (10%), three of 62 (5%) and 19 of 70 (27%) were positive for the vaccine-related pneumococcal serotypes among the Pnc-D, Pnc-T and placebo recipients, respectively (P = 0.001 for Pnc-D versus placebo; P=0.014 for Pnc-T versus placebo). Most of the antibiotic-resistant isolates from the nasopharynx belonged to the vaccine-related serotypes. These studies showed clearly that conjugate pneumococcal vaccines could reduce the carriage of S. pneumoniae and resistant S. pneumoniae of the serotypes included in the vaccines. Obaro et al [42Obaro SK Adegbola RA Banya WA Greenwood BM Carriage of pneumococci after pneumococcal vaccination.Lancet. 1996; 348: 272Abstract Full Text Full Text PDF Scopus (277) Google Scholar] raised an important issue regarding the effect of conjugate pneumococcal vaccines on carriage. The research group in the Gambia studied the effect of the pentavalent pneumococcal vaccine (which included serotypes 6B, 14, 18C, 19F and 23F) conjugated to CRM197 (a non-toxic mutant of diphtheria toxin) on S. pneumoniae carriage in infants. In the Gambia, simultaneous carriage of multiple serotypes was common. Under these circumstances, Obaro et al observed two opposite effects of the vaccine on carriage. (1) The serotypes included in the vaccine were commonly found in children aged 21 months who had not received any pneumococcal vaccine previously (the carriage rate was 83–90%). In contrast, those who had received the pentavalent conjugate vaccine at 2, 3 and 4 months of age carried the vaccine-related serotypes significantly less frequently (50%; P value versus controls <0.005). (2) Contrary to the effect observed with the vaccine serotypes, the other pneumococcal serotypes were carried significantly more often by the vaccine recipients than by the controls (77% versus 43%; P<0.005). This preliminary observation on the promotion of carriage of S. pneumoniae serotype not included in the vaccine by conjugate vaccine was provocative and raised several questions and concerns. Shortly after the observation from the Gambia, reduction of the serotypes included in the conjugate vaccine and replacement by other serotypes after immunization were confirmed by South African researchers, who immunized infants at ages 6, 10 and 14 weeks with a nine-valent (serotypes 1, 4, 5, 6B, 9V, 14, 18C, 19F and 23F) pneumococcal vaccine conjugated to CRM197 [43Mbelle N Wasas A Huebner R Kimura A Chang I Kimura A Immunogenicity and impact on carriage of 9‐valent preumococcal conjugate given to infants in Soweto, South Africa [abstract LB21].in: Abstracts of the 37th Interscience Conference on Antimicrobial Agents and Chemotherapy, Toronto. American Society for Microbiology, Washington DC1997: 13Google Scholar]. Our group undertook an extensive study to determine if carriage in toddlers attending day-care centers (which, as detailed above, are probably the main location associated with amplification and spread of resistant S. pneumoniae in the community) is affected by immunization. In a double-blind prospective randomized study involving 264 toddlers during their second and third years of life, we immunized 132 toddlers with a nine-valent (containing serotypes 1, 4, 5, 6B, 9V, 14, 18C, 19F, 23F) pneumococcal vaccine conjugated to CRM197 [44Dagan R Givon N Yagupsky P et al.Effect of a 9‐valent pneumococcal vaccine conjugated to CRM197 (PncCRM9) on nasopharyngeal carriage of vaccine type and non‐vaccine type S. pneumoniae (Pnc) strains among day‐care center DCC) attendees [abstract G‐52).in: Abstracts of the 38th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, California. American Society for Microbiology, Washington DC1998: 299Google Scholar]. A nasopharyngeal culture was obtained before and once monthly after immunization for 1 year, and bi-monthly during the second year. Although the study will be completed only during the first quarter of 1999, an interim analysis was done after 18 months of follow-up by a statistician not belonging to the study group [44Dagan R Givon N Yagupsky P et al.Effect of a 9‐valent pneumococcal vaccine conjugated to CRM197 (PncCRM9) on nasopharyngeal carriage of vaccine type and non‐vaccine type S. pneumoniae (Pnc) strains among day‐care center DCC) attendees [abstract G‐52).in: Abstracts of the 38th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, California. American Society for Microbiology, Washington DC1998: 299Google Scholar]. At this time, 3646 cultures were obtained, with 2364 (68%) cultures being positive for S. pneumoniae. Of the 2364 pneumococcal isolates, 53%, 38% and 9% were resistant to at least one antibiotic, non-susceptible to penicillin and resistant to ≤3 drugs, respectively. The interim analysis showed the following points: (1) the carriage of pneumococci included in the vaccine was significantly reduced in vaccinees compared with controls; (2) the carriage of antibiotic-resistant pneumococci was significantly reduced in vaccinees compared with controls; (3) the total carriage of S. pneumoniae was significantly reduced compared with controls; and (4) the carriage of pneumococcal serotypes not included in the vaccine was significantly increased compared with controls (Figure 6). The effect was observed mainly in those starting the study during their second year of life, and was almost not significant for those starting the study during the third year of life (not shown in the figure). What is the significance of the effect of conjugate vaccines on pneumococcal carriage observed so far? It is certain that some news is good: (1) the reduction of carriage of S. pneumoniae and resistant S. pneumoniae of the vaccine types suggests a potential for a strong herd immunity effect, permitting reduction of spread of the serotypes most commonly associated with disease and antibiotic resistance in the community; (2) the strong mucosal effect of the vaccine expressed by the reduction of nasopharyngeal carriage suggests that children may also be protected from otitis media, and thus permits us to be optimistic and to hope that the high efficacy against invasive pneumococcal infections shown recently with one conjugate vaccine [45Black S Shinefield H Ray P et al.Efficacy of heptavalent conjugate pneumococcal vaccine (Wyeth Lederle) in 37,000 infants and children: results of the northern California Kaiser Permanente efficacy trial [abstract LB9].in: Abstracts of the 38th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, California. American Society for Microbiology, Washington DC1998: 23Google Scholar] may not be confined to invasive infections, but may also show, in the future, efficacy against the much more common mucosal infections; and (3) the effect of the vaccines on carriage may allow us in future to use reduction of carriage as an important surrogate of efficacy, if no placebo-controlled efficacy studies are allowed after introduction of pneumococcal conjugate vaccines to the immunization programs. However, some questions have been raised which should be answered before the optimism becomes reality. (1) Does the increase in the carriage of the serotypes not included in the vaccine represent a future threat? In other words, will it be associated with increased pneumococcal disease with these serotypes? (2) Will resistance spread to the serotypes not included in the vaccine that will now be carried more often? Certainly, these questions are important and cannot be answered in the immediate future. However, it is biologically plausible to assume that the replacement of carriage will not be associated with a replacement in disease, at least not to the same extent. The serotypes included in the vaccines, and especially the ones most resistant to antibiotics, are also most often less immunogenic in children and can therefore be carried for long periods. This phenomenon allows them to be exposed to antibiotics for a longer period of time and thus to become more resistant. It can be speculated that the serotypes not included in the vaccine, which are also more immunogenic and therefore are carried for a shorter period of time, will have consequently less chance to become antibiotic resistant. However, antibiotic resistance does also exist among some serotypes not included in the vaccine, especially in serotypes such as 6A and 19A, which are also quite important in disease, especially in otitis media. Although we do expect cross-protection between 6B and 6A, such cross-protection may not occur with 19F and 19A. Thus, some doubts still remain in regard to the beneficial effect of the conjugate vaccines on the pneumococcal nasopharyngeal flora, and it is possible that in the future some additional serotypes that are antibiotic resistant and cause disease will be added to the currently developed conjugate vaccine. In conclusion, carriage of antibiotic-resistant S. pneumoniae is frequent and is increasing worldwide, especially among infants and toddlers in crowded conditions. The use of vaccines may be one of the most efficient ways to fight this phenomenon, but other strategies, such as restriction of antibiotic use, are still extremely important.