Streptococcus pneumoniae (SP) is the main etiologic agent of community-acquired pneumonia, and acute otitis media in children, especially in those younger than 5 years of age. Human nasopharyngeal (NP) carriage is the main site of acquisition of pathogenic bacteria in the respiratory tract.1–3
NP colonization with SP is a prerequisite for local and systemic disease. Several studies conducted in Israel,3 South Africa4, Pakistan,5 Canada6 and New Guinea7 confirm that NP colonization with SP, in young children, reflects the serotype distribution and antimicrobial susceptibility of invasive disease isolates.
The main objective of this study was to determine whether serotype distribution and antimicrobial susceptibility of SP isolated from the nasopharynx of children correlated with serotype distribution and antimicrobial susceptibility of invasive isolates. The second objective was to assess the serotype distribution found in NP and invasive pneumococcal disease (IPD) isolates and calculate serotype coverage for the commercial SP heptavalent conjugated vaccine with serotypes 4, 6B, 9V, 14, 18C, 19F, 23F (7V), the investigational vaccine that contains the 7 serotypes plus 1, 5 and 7F (10V) and the other investigational vaccine that contains the 10 serotypes plus 3, 6A and 19A (13V) vaccines.
This study was carried out at the pediatric emergency services and pediatrics units of 3 hospitals located in Sao Paulo, Brazil, in patients who had not received pneumococcal vaccine.
Children aged 3 months to 5 years with upper respiratory infections presenting to the pediatric emergency services between June 1997 and May 2001 were eligible for the study. The NP samples were obtained according with the WHO recommendations.8 For collecting the NP samples, a flexible sterile cotton-tip swab was introduced into the child's nostril to a depth that corresponded to two-thirds of the distance between the nose and the earlobe. The swab was inoculated onto 5% sheep blood agar plate containing 5 μg/mL gentamicin, and taken to the bacteriology laboratory on the same day. Alpha-hemolytic colonies exhibiting morphologic characteristics suggestive of S. pneumoniae were isolated. Identification was confirmed by inhibition with optochin and by bile solubility.
Isolates were routinely screened for penicillin resistance with an oxacillin 1 μg disk by the Kirby-Bauer disk diffusion method. Organisms with a zone of inhibition <20 mm were confirmed as penicillin nonsusceptible (PNSP) by minimal inhibitory concentration (MIC) using the penicillin E-test and defined as susceptible, intermediate resistance or high resistance in accordance with Clinical and Laboratory Standards Institute (formally known as NCCLS) guidelines.
All SP strains were serotyped by the Quellung test using sera from the Staten Seroinstitut, Copenhagen, Denmark, at the Instituto Adolfo Lutz, São Paulo, Brazil.
To compare serotypes and penicillin susceptibility data we selected children aged 3 months to 5-year-old diagnosed with IPD, admitted in the same hospitals between 1996 and 2001 identified by review of microbiology records between 1996 and 2001.
Univariate analysis was performed by the χ2 test with Yates correction to confirm the significant differences between the groups of colonized and noncolonized children. P < 0.05 were considered significant. Fisher's exact test was used when expected cell values were <5.
Proportion of coverage by the heptavalent PCV and the investigational 10 and 13v PCV vaccines were calculated by proportion of serotypes included in the vaccines of all serotypes detected in colonized and infected children.
NP samples were obtained from 520 children, 225 between 3 months and 2 years age and 218 between 2 and 5 years. SP was recovered from 181 children (35% of total). From this total, 109 were from children 3 months to 2 years of age and 72 from children 2 to 5 years of age.
Between 1997 and 1998, NP swabs were obtained from 440 patients. SP was isolated in 139 patients (32%). Between 2000 and 2001, NP swabs were obtained from 80 patients and SP was found in 42 patients (53%). NP colonization was found in 109 (35%) of children 3 months to 2 years of age and in 72 (32%) of those 2–5 years of age.
During the study period, 105 invasive infections were diagnosed in children less than 5 years of age. A total of 55 and 50 IPD isolates were identified in 1996–1999 and 2000–2001, respectively. In the first period, 50% of the patients were younger than 2-year-old. In the second period, 64% were younger than 2 years. The sites were pleural fluid, blood culture, CSF and articular fluid (32, 36, 34 and 3 patients, respectively). The diagnoses were pneumonia in 52 children, meningitis in 34, arthritis in 4 and bacteremia in 15.
Twenty (14%) and 18 (43%) patients were colonized by PNSP in 1997–1998 and 2000–2001, respectively. All strains exhibited intermediate susceptibility. Among the invasive infections PNSP was found in 14 of 55 (25.4%) of patients in 1997–1998 and 17 of 50 (34%) of patients in 2000–2001. All strains isolated in the first study period exhibited intermediate resistance. High-level resistance was seen in 6 strains (35% of the PNSP) in the second study period.
We identified serotypes in 162 of the 181 SP in NP isolates (120 in the first period and 42 in the second period) and 105 SP in IPD isolates (55 in the first period and 50 in the second period). Serotype distribution for NP and IPD isolates is shown on Table 1.
The most frequent serotypes obtained from the nasopharynx were 14, 6B, 23F, 6A and 19F, accounting for 52.8% of all NP isolates. The serotypes 20, 23F and 11A were found only in the first period and serotype 4 was found only in the second period.
Serotype 14 was the most frequent IPD serotype in the 2 periods accounting for 35.5% of all IPD isolates. Serotypes 14, 1, 5 and 23F accounted for 72.5% of the IPD isolates and were the 4 most frequent serotypes in both periods of the study. Serotypes 14, 1 and 5 were significantly more likely to cause invasive disease and serotypes 6A and 11A were significantly more likely to be present only as colonizers (Table 1).
In pneumonia, the most frequent serotypes were 14 (24), 1 (8) and 6B (4). In meningitis the most frequent serotypes were 23F (9), 14 (6) and 5 (6).
Serotype coverage by the 7V vaccine, by the the 10V vaccine and by the 13V vaccine for NP and IPD isolates is shown in Table 1.
Data comparing antibiotic susceptibility between invasive and carriage S. pneumoniae isolates are limited. Kellner et al6 in Canada and Lehmann et al7 in Papua New Guinea studied the prevalence of reduced penicillin susceptibility in NP carriage and invasive infections found no difference between the 2 groups.
There are differences in the prevalence and rank order of serotypes between invasive and noninvasive collections and these differences vary depending on the population and geographic location. In our study, the most frequent serotypes obtained from NP were 14, 6B, 19F, 6A and 23F. The most frequent serotypes obtained from PII were 14, 1, 23F and 5. In our study, serotypes 1 and 5 were rare among NP carriage isolates, in contrast to the high prevalence of those serotypes among the isolates causing pediatric invasive disease. It has been well documented that serotypes 1 and 5 are among the most common IPD serotypes in Brazil.10 It has been hypothesized that, because of their virulence, serotypes 1 and 5 have a transient and fast passage through the nasopharynx before reaching the blood stream.2 Laval et al9 in a report from Goiania, Brazil, reported a higher coincidence between serotypes of NP and from IPD isolates probably because in this report the rate of infections by serotype 1 was low. In our series most of infections caused by serotype 1 were pneumonia.
The differences in the prevalence and rank order of serotypes between invasive and noninvasive collections vary depending on the population and geographic location. In addition, because PNSP isolates are linked to a limited number of serotypes, any valid comparison of S. pneumoniae isolates from different sites must take serotypes into account.
S. pneumoniae is the most common cause of death worldwide due to a vaccine preventable illness. Vaccination is the best solutions to this problem. Effective vaccines that include serotypes 1 and 5 would be very beneficial preventing more than 90% of IPD cases. Until these investigational vaccines become available, our study demonstrates that we can prevent the majority (66%) of IPD cases in Sao Paulo (Brazil) with the use of the 7V vaccine.
1. Willians JÁ, Gouvs E, Bosghi-Pinto C, Brice J. Dye C. Estimates of world-wide distribution of child deaths from acute respiratory infections. Lancet Infect Dis.
2. Bogaert D, De Groot R, Hermans PW. Streptococcus pneumoniae colonization: the key to pneumococcal disease. Lancet Infect Dis
3. Dagan R, Leibovitz E, Greenberg D, Yagupsky P, Fliss DM, Leiberman A. Dynamics of pneumococcal nasopharyngeal colonization during the first days of antibiotic treatment in pediatric patients. Pediatr Infect Dis J
4. Klugman KP, Koornhof HJ, Wasas A, Storey K, Gilbertson I. Carriage of penicillin-resistant pneumococci. Arch Dis Child
5. Mastro TD, Nomani NK, Ishaq Z, et al. Use of nasopharyngeal isolates of Streptococcus pneumoniae and Haemophilus influenzae from children in Pakistan for surveillance for antimicrobial resistance. Pediatr Infect Dis J
6. KellnerJD, Mcgeer A, Cetron M, Low DE, Butler JC, Matlow A. The use of Streptococcus pneumoniae nasopharyngeal isolates from healthy children to predict features of invasive disease
. Pediatr Infect Dis J.
7. Lehmann 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
8. O Brien K, Nohynek H, and the Pneumococcal Vaccine Trials Carriage Group. Report from a WHO Working Group: Standard method for detecting upper respiratory carriage of Streptococcus pneumoniae. Pediatr Infect Dis J.
9. Laval CB, de Andrade AL, Pimenta FC, et al. Serotypes
of carriage and invasive isolates of Streptococcus pneumoniae in Brazilian children in the era of pneumococcal vaccines. Clin Microbiol Infect.
10. Di Fabio JL, Castaneda E, Agudelo CI, et al. Evolution of Streptococcus pneumoniae serotypes
and penicillin susceptibility in Latin America, Sireva-Vigia Group, 1993–99. PAHO Sireva-Vigia Study Group. Pan American Health Organization. Pediatr Infect Dis J