Nurith Porat

Nasopharyngeal Carriage of Streptococcus pneumoniae by Adults and Children in Community and Family Settings

The rate of Streptococcus pneumoniae carriage among adults was compared with that among children (age, < or =6 years) in the same population. Nasopharyngeal culture results for 1300 adults and 404 children were analyzed. S. pneumoniae was carried by only 4% of the adults, compared with 53% of children in the same community. Young age, day care center attendance, having young siblings, and no antibiotic use during the month before screening were associated with the high carriage rate among children, whereas the only risk factor associated with carriage among adults was the presence of a respiratory infection on the screening day. S. pneumoniae serotype distribution and antibiotic resistance patterns differed between adults and children. Isolates of the same serotype--even of the same clone--differed in their antibiotic susceptibility patterns between children and adults. In a subanalysis of 151 pairs of children and their parents and of 32 pairs of siblings, intrafamilial transmission of S. pneumoniae could not be demonstrated.

Introduction and Proliferation of Multidrug-Resistant Streptococcus pneumoniae Serotype 19A Clones That Cause Acute Otitis Media in an Unvaccinated Population

BACKGROUND Introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) in the United States in 2000 was temporally associated with an increase in the incidence of disease caused by Streptococcus pneumoniae serotype 19A (Sp19A) and with increasing drug resistance within this serotype. A causative role of PCV7 was speculated. We prospectively studied the dynamics of acute otitis media (AOM) caused by Sp19A in southern Israel before the introduction of PCV7. METHODS AOM in children < 5 years old undergoing tympanocentesis during 1999-2006 was studied. Antibiotic prescriptions for approximately 20% of children < 5 years old were recorded. Sp19A isolates were studied for antibiotic-resistance and pulsed-field gel electrophoresis patterns; multilocus sequence typing of representative isolates was compared with that of international clones. RESULTS Sp19A caused 438 (9.8%) of 4449 pneumococcal AOM episodes, increasing by 63.1% from 1999-2001 (mean +/- SD, 8.4% +/- 0.8%) to 2004-2006 (mean +/- SD, 13.7% +/- 0.9%) among Bedouin children, who were characterized by overcrowding and high antibiotic use. Penicillin, erythromycin, and multidrug resistance increased from < 10% to 78.6%, 50.0%, and 50.0%, respectively (P < .001), and was associated with the introduction and proliferation of 2 multidrug-resistant clones that were not previously associated with multidrug resistance. This was temporally associated with the introduction of and rapid increase in azithromycin use and the frequent use of oral cephalosporins. CONCLUSIONS The introduction and proliferation of multidrug-resistant Sp19A occurred before the introduction of PCV7. The increasing proportion of antibiotic-resistant Sp19A suggests that antibiotic use plays an important role in the community.

Acquisition, Carriage, and Transmission of Pneumococci with Decreased Antibiotic Susceptibility in Young Children Attending a Day Care Facility in Southern Israel

The prevalence and transmission of antimicrobial drug-resistant pneumococci was studied in 48 children attending a day care facility in southern Israel. Nasopharyngeal cultures were obtained every 2 weeks for 10 months, and antibiotic susceptibility of isolates was determined by disk diffusion and E-test. Relatedness of isolates was investigated by capsular typing, ribotyping, and arbitrarily primed polymerase chain reaction. Pneumococci were recovered during 362 (63%) of 573 fortnights, and 219 (60%) of these isolates showed decreased susceptibility to at least one drug; 154 (43%) were intermediately susceptible to penicillin and 51 (14%) were multiresistant. Combining the different typing methods showed that a limited number of clones circulated in the facility. Clones exhibiting decreased antibiotic susceptibility (especially 23F, intermediately susceptible to penicillin and resistant to trimethoprim-sulfamethoxazole, and multiresistant 6B) were more frequently isolated and persisted longer than did fully susceptible clones. By multivariate analysis, carriage of organisms with decreased antibiotic susceptibility was associated with young age, female sex, winter season, and exposure to antimicrobial drugs during the previous month.

Site-specific disease potential of individual Streptococcus pneumoniae serotypes in pediatric invasive disease, acute otitis media and acute conjunctivitis

Background: Recent studies have shown that some Streptococcus pneumoniae serotypes possess a higher potential to cause invasive disease than others. However, it is unknown whether disease potential for specific serotypes is similar for mucosal disease. Our objective was to assess the disease potential of individual S. pneumoniae serotypes causing invasive pneumococcal disease (IPD), acute otitis media (AOM) and acute conjunctivitis (AC) in children. Methods: Serotypes of pneumococcal isolates from children with IPD, AOM and AC were compared with those carried by healthy children aged <3 years. All children resided in the same area and were studied during the same period. Odds ratios for disease were calculated for each diagnosis following multivariate analysis, including gender, age, ethnic group, previous antibiotic treatment and year variability. Results: A total of 5500 isolates were collected: 189 from blood or cerebrospinal fluid, 3200 from middle ear fluid, 348 from conjunctiva and 1763 from nasopharynx of healthy children. A significant positive association with IPD was demonstrated for serotypes 1, 5 and 12F; with AOM for serotypes 1, 3, 5, 12F, 19A and 19F; and with AC for serotype 3 and nontypeable S. pneumoniae. A significant negative association with IPD was demonstrated for nontypeable S. pneumoniae and with AOM for serotypes 6A, 6B, 15A and nontypeable S. pneumoniae. Conclusions: Our results reflect the importance of the polysaccharide capsule in site-specific disease potential and provide useful information regarding disease potential of nonvaccine serotypes shown to be involved in carriage replacement after vaccination with the 7-valent conjugate vaccine.

Comparative Immunogenicity and Efficacy of 13-Valent and 7-Valent Pneumococcal Conjugate Vaccines in Reducing Nasopharyngeal Colonization: A Randomized Double-Blind Trial

BACKGROUND The 13-valent pneumococcal conjugate vaccine (PCV13) was licensed to replace the 7-valent pneumococcal conjugate vaccine (PCV7) based on serological noninferiority criteria. To date no randomized PCV13 pediatric trial has included clinical endpoints. METHODS This randomized double-blind trial compared the impact of PCV13 versus PCV7 on nasopharyngeal (NP) colonization and immunogenicity. Healthy infants were randomized (1:1) to receive PCV7 or PCV13 at ages 2, 4, 6, and 12 months; NP swabs were collected at 2, 4, 6, 7, 12, 13, 18, and 24 months, and blood was drawn at 7 and 13 months. Rates of NP acquisition and prevalence, and serotype-specific immunoglobulin G (IgG) concentrations were assessed. RESULTS The per protocol analysis population included 881 PCV13 and 873 PCV7 recipients. PCV13 significantly reduced NP acquisition of the additional PCV13 serotypes 1, 6A, 7F, and 19A; the cross-reacting serotype 6C; and the common PCV7 serotype 19F. For serotype 3, and the other PCV7 serotypes, there were no significant differences between the vaccine groups. There were too few serotype 5 events to draw inference. The impact on prevalence at predefined time points was similar to that observed with NP acquisition. PCV13 elicited significantly higher IgG responses for PCV13 additional serotypes and serotype 19F, and similar or lower responses for 6/7 PCV7 serotypes. CONCLUSIONS PCV13 resulted in lower acquisition and prevalence of NP colonization than PCV7 did for 4 additional PCV13 serotypes, and serotypes 6C and 19F. It was comparable with PCV7 for all other common serotypes. These findings predict vaccine effectiveness through both direct and indirect protection. CLINICAL TRIALS REGISTRATION NCT00508742.

Emergence of Penicillin-Nonsusceptible Streptococcus pneumoniae Clones Expressing Serotypes Not Present in the Antipneumococcal Conjugate Vaccine

BACKGROUND Penicillin-nonsusceptible Streptococcus pneumoniae isolates are confined mainly to a few serogroups. Capsular transformation may serve as a mechanism for spreading antibiotic resistance to new serotypes. METHODS Antibiogram and molecular typing, by pulsed-field gel electrophoresis (PFGE), were performed on 46 nasopharyngeal and middle ear fluid (MEF) isolates expressing serotype 11A, 45 MEF isolates expressing serotype 15B/C (recovered during 1998-2003 from Israeli children <5 years old), and 57 MEF isolates expressing serotype 19F (recovered during 1998-2001 from Costa Rican children <7.5 years old). RESULTS PFGE patterns showed that 49 (86%) of 57 serotype 19F isolates and 19 (41%) of 46 serotype 15B/C isolates were closely related. The vast majority of these isolates (80% of serotype 19F and 100% of serotype 15B/C isolates) were nonsusceptible to penicillin. Multilocus sequence typing (MLST) data show that the serotype 15B/C isolates belonged to the ST346 cluster, whereas the serotype 19F isolates were a single-locus variant of ST346. For serotype 11A isolates, PFGE patterns and MLST analysis showed that 8 (80%) of the 10 penicillin-nonsusceptible isolates belonged to a single clone--namely, ST156--which was identical to the international Spain9V-3 clone. CONCLUSIONS Penicillin-nonsusceptible pneumococcal clones of serotypes not related to those included in the 11-valent conjugate vaccines may derive from capsular transformation of vaccine-related serotypes. Of particular concern was the detection of serotype 11A variants of the successful international Spain9V-3 clone. This phenomenon, although seemingly rare at present, can have implications for the long-term effectiveness of the conjugate vaccines.

An Outbreak of Streptococcus pneumoniae Serotype 1 in a Closed Community in Southern Israel

An outbreak of Streptococcus pneumoniae serotype 1 occurred in a closed community that was characterized by poverty and crowding. Vaccine was administered to individuals aged >2 years; no new cases occurred among vaccine recipients. Six weeks after vaccination, carriage of serotype 1, but not of other serotypes, decreased 8.8-fold. This suggests that the reduction in serotype 1 carriage reflects the natural course of the outbreak rather than a vaccine effect. Polysaccharide vaccine may be helpful in terminating pneumococcal outbreaks but may not affect pneumococcal carriage.

Antibiotic Treatment in Acute Otitis Media Promotes Superinfection with Resistant Streptococcus pneumoniae Carried before Initiation of Treatment

Antibiotic-resistant pneumococci are difficult to eradicate from middle ear fluid (MEF) and the nasopharynx (NP). Bacteriologic eradication from the NP and MEF during acute otitis media (AOM) by 3 common antibiotic drugs was prospectively evaluated. In 19 (16%) of 119 MEF culture-positive patients, an organism susceptible to the treatment drug (Haemophilus influenzae, Streptococcus pneumoniae, or both) was isolated from the initial MEF, whereas resistant S. pneumoniae was present in the NP; in 9 (47%) patients, the initial resistant NP organism (identified by serotyping, resistance to the administered drug, and pulsed-field gel electrophoresis) replaced the susceptible MEF organism within only a few days after initiation of treatment. In regions where resistant pneumococci are prevalent, antibiotics may not only fail to eradicate the organisms, but they may often induce MEF superinfection with resistant pneumococci initially carried in the NP. This is an important mechanism by which, in recently treated patients, AOM infections often become refractory to treatment.

Marked Differences in Pneumococcal Carriage and Resistance Patterns between Day Care Centers Located within a Small Area

Carriage rates of Streptococcus pneumoniae and their antibiotic resistance, capsular types, and genetic patterns were studied among 264 children aged 12-35 months attending 8 day care centers located within a 2.5-mile radius in the same city. Nasopharyngeal cultures were obtained within a 2-month interval from all 264 children. Significant differences in each of the studied characteristics were found between day care centers, and each day care center had a unique pattern of the carried pneumococci. Our findings show that day care centers are independent microenvironments and emphasize their role in the transmission and augmentation of antibiotic-resistant S. pneumoniae in the community.

Differences in membrane fluidity and fatty acid composition between phenotypic variants of Streptococcus pneumoniae.

Phase variation in the colonial opacity of Streptococcus pneumoniae has been implicated as a factor in the pathogenesis of pneumococcal disease. This study examined the relationship between membrane characteristics and colony morphology in a few selected opaque-transparent couples of S. pneumoniae strains carrying different capsular types. Membrane fluidity was determined on the basis of intermolecular excimerization of pyrene and fluorescence polarization of 1,6-diphenyl 1,3,5-hexatriene (DPH). A significant decrease, 16 to 26% (P < or = 0.05), in the excimerization rate constant of the opaque variants compared with that of the transparent variants was observed, indicating higher microviscosity of the membrane of bacterial cells in the opaque variants. Liposomes prepared from phospholipids of the opaque phenotype showed an even greater decrease, 27 to 38% (P < or = 0.05), in the pyrene excimerization rate constant compared with that of liposomes prepared from phospholipids of bacteria with the transparent phenotype. These findings agree with the results obtained with DPH fluorescence anisotropy, which showed a 9 to 21% increase (P < or = 0.001) in the opaque variants compared with the transparent variants. Membrane fatty acid composition, determined by gas chromatography, revealed that the two variants carry the same types of fatty acids but in different proportions. The trend of modification points to the presence of a lower degree of unsaturated fatty acids in the opaque variants compared with their transparent counterparts. The data presented here show a distinct correlation between phase variation and membrane fluidity in S. pneumoniae. The changes in membrane fluidity most probably stem from the observed differences in fatty acid composition.