Two hundred forty-two subjects aged less than 6 years attending two public institutions between March and June 2010 were included in this study. Their median age was 3 years old (interquartile range: 1.6 – 4.5 years old), 129 of them (53.3%) were male and 113 (46.7%) were female.
A total of 121 pneumococcal isolates was recovered from 119 children, revealing an overall colonization rate of 49.2%. Two phenotypically distinct pneumococcal colonies were detected in the respective cultures obtained from two subjects, indicating co-colonization. The prevalence of pneumococcal carriage was 42.1% (59/140) among children at the PH and 58.8% (60/102) among those at the DCC.
The demographical and clinical characteristics of the 242 children included in this study are shown in Table . The characteristics that showed greater differences between carriers and non-carriers were day care attendance and cohabiting with siblings under 6 years of age.
Demographic and clinical characteristics of the 242 children enrolled in the present study
Twenty-five serotypes were detected among 117 (96.7%) of the 121 pneumococcal isolates recovered. The cpsA pneumococcal identification control gene was not detected among the four non-typeable (NT) isolates, but their identification was confirmed by amplification of the lytA gene. The prevalent serotypes identified were 6B (15.7%), 19F (12.4%), 6A (9.9%), 14 (9.1%), 15C (8.3%) and 23F (5.8%). Table shows the distribution of serotypes according to the institution.
Distribution of capsular types among 121 Streptococcus pneumoniae isolates recovered from the nasopharynx of children living in a large metropolitan area in Southeastern Brazil
Serotype 19F (21.7%; 13/60) was the prevalent type among carriers from the PH and the presence of respiratory symptoms such as coryza/sneezing and cough/expectoration showed to be associated with colonization by pneumococci belonging to this serotype. On the other hand, serotype 6B (23%; 14/61) was the most frequent among children attending the DCC, mainly in children aged ≥ 2 years. Regarding simultaneous colonization, in both the subjects, one of the isolates was NT and the remaining isolates belonged to serotypes 6B or 19A. Additionally, the serotypes recovered from the two pneumococcal carriers who had received only the first primary immunization dose of the PCV7, both attending the DCC, were 6B and 15C.
All the isolates were susceptible to clindamycin, levofloxacin, rifampicin and vancomycin. Susceptibility to the other five antimicrobial agents tested varied, with the highest percentage of non-susceptibility being observed for sulphamethoxazole-trimethoprim (51.2%; 62/121), including 38.8% resistant and 12.4% intermediate isolates.
Non-susceptibility to penicillin was detected in 27.3% (33/121) of the isolates and MICs ranged from 0.12 to 4.0 μg/ml. Following the current CLSI criteria for oral penicillin V, 22 (18.2%) isolates presented intermediate MICs (Pen-I) and 11 (9.1%) showed MICs indicative of resistance to penicillin (Pen-R). According to the CLSI breakpoints for parenteral penicillin (meningitis), all 33 isolates would be considered Pen-R. However, for parenteral penicillin (nonmeningitis), only 11 (9.1%) isolates would be Pen-I and none would be Pen-R (Figure ).
Figure 1 Distribution of penicillin non-susceptible (MIC > 0.6 μg/ml) Streptococcus pneumoniae considering the different MIC breakpoints. Pen, penicillin; R, resistant; I, intermediate. MIC, Minimum Inhibitory Concentrations. Adopted MIC breakpoints: (more ...)
Penicillin non-susceptible pneumococci (PNSP) were more common among children attending the PH, being this characteristic strongly associated with serotypes 14 and 23F (Table ). Nine (81.8%) of the 11 serotype 14 isolates were PNSP and all of them presented the highest penicillin MIC observed in this study (4.0 μg/ml). Likewise, all seven serotype 23F isolates were non-susceptible to penicillin, with MICs ranging from 0.18 μg/ml to 0.25 μg/ml. In addition, all the symptoms investigated in this study were strongly associated with PNSP carriage, including fever, coryza/sneezing, cough/expectoration, fatigue/breathlessness and hipoactivity.
Characteristics of penicillin non-susceptible (MIC > 0.6 μg/ml) Streptococcus pneumoniae serotypes recovered from nasopharyngeal carriers in a large metropolitan area in Southeastern Brazil
Two isolates were non-susceptible to erythromycin, showing MICs of 2.0 μg/ml and 4.0 μg/ml. Both isolates were obtained from children at the PH (each one from a different child), belonged to serotype 6A, presented the M phenotype and harbored the mef(A/E) gene. Both isolates were also PNSP, with MICs of 0.25 μg/ml.
Resistance to tetracycline was observed in only two (1.7%) pneumococcal isolates (one serotype 6B and another NT) that colonized simultaneously the same child attending the DCC. Eight (6.6%) additional isolates were intermediate to tetracycline.
Four (3.3%) isolates were resistant to chloramphenicol, and two of them belonged to serotype 6B. The other two were NT and represented the only multiresistant isolates detected in this study, since they were also resistant to sulphamethoxazole-trimethoprim and non-susceptible to penicillin (MICs of 0.25 μg/ml).
Among the 140 children attending the PH that were included in the present study, seven (5.0%) were hospitalized with pneumonia, and four of them were also nasopharyngeal pneumococcal carriers. The isolates recovered from these individuals belonged to serotypes 19F (n=3) and 14 (n=1). All of them, except one serotype 19F isolate, were PNSP. However, no microorganisms were recovered from the blood culture of these patients, and after treatment using β-lactams the children had their health restored.