Longitudinal study on pneumococcal carriage during the first year of life in Bangladesh.

BACKGROUND: The strong herd immunity effect and the serotype replacement associated with the use of the pneumococcal conjugate vaccine have highlighted the importance of asymptomatic pneumococcal carriage. To describe the development of pneumoccoccal carriage in a developing country setting we carried out a longitudinal pneumococcal carriage study in Bangladesh. METHODS: Ninety-nine children, born in Savar, Bangladesh between May 2000 and April 2001, were enrolled in the study with their families. Nasopharyngeal samples were collected at prescheduled 2-4 week intervals from the index children and from their family members. The nasopharyngeal swabs were cultured for pneumococcal growth and pneumococci were identified and serotyped by standard methods. RESULTS: We collected 1459 samples (92% of those planned) from the 99 index children and 2865 samples from other family members. The data showed high point prevalences of pneumococcal carriage among newborns (40-50% from 8 weeks of age on), a rapid pneumococcal acquisition with age (50% of the children had been colonized by pneumococci at least once by the age of 8 weeks) and a wide range of different serogroups/types (SGT). SGT 6 and 19 accounted for 35% of the pneumococci isolated from children <1-year-old, followed by SGT 15, 23, and 10 for a total of 56%. The SGT distribution in children up to 9-year-old was similar to that among the <1 year olds, with SGT 6 and 19 predominating. Older children and adults differed from the younger children by not having clearly predominating SGTs. CONCLUSIONS: The features found in our study are typical of pneumococcal carriage in developing countries. We believe that results from longitudinal modeling of carriage based on these extensive data can have wide geographic application.

The value of nasopharyngeal culture in predicting the etiology of acute otitis media in children less than two years of age.

BACKGROUND: In selecting treatment of acute otitis media (AOM), knowledge of its etiology would be valuable. We revisited the possibility to use the nasopharyngeal culture of Streptococcus pneumoniae (Pnc) and Haemophilus influenzae (Hi) for predicting their presence in the middle ear fluid (MEF) during AOM. METHODS: The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of bacterial culture of the nasopharyngeal aspirate (NPA) in predicting the presence of the same pathogen in the MEF were assessed during AOM events among children followed from 2 to 24 months of age. RESULTS: The data comprised 586 AOM events. For Pnc, the sensitivity and NPV were high, 99% (95% confidence interval = 95-100%) and >99% (97-100%), respectively. The specificity and PPV were relatively low, 63% (57-68%) and 50% (43-56%). For Hi, the sensitivity and the NPV were lower (77%, 69-83% and 93%, 90-95%) than for Pnc, but the specificity and the PPV were higher (88%, 85-91% and 64%, 56-71%). The quantity of Pnc and Hi in the NPA was clearly related to their presence in the MEF. If both Pnc and Hi were found in the nasopharynx, Hi was more likely cultured from MEF. CONCLUSION: Together with clinical and epidemiologic features of AOM, the nasopharyngeal culture can be helpful in selecting specific antimicrobial therapy.

Field evaluation of the chessboard modification for serotyping of Streptococcus pneumoniae in a small laboratory in Bangladesh.

The chessboard modification of the quellung method for serotyping Streptococcus pneumoniae (Pneumococcus) was introduced in the Gonoshasthaya Vaccine Research Laboratory, a small laboratory in Bangladesh. We applied initial bench-side training and subsequent continuous surveillance and quality assurance as approaches for good laboratory practice. Results obtained a this laboratory on 1,101 consecutive isolates had satisfactory sensitivity (85.1-100%) and specificity (97.9-99.9%) for serotyping the 10 most common serogroups/types of pneumococci when compared with the results obtained in the Finnish reference laboratory for pneumococcal serotyping at the National Public Health Institute. We conclude that serotyping of pneumococci by the chessboard method can be introduced into a small laboratory by providing basic bacteriologic skills, adequate initial training, and continuous external support.

Real-time pneumolysin polymerase chain reaction with melting curve analysis differentiates pneumococcus from other alpha-hemolytic streptococci.

The majority of pneumococcal isolates can be identified by the conventional methods based on phenotypic characteristics. Occasionally, however, the differentiation of alpha-hemolytic streptococci from pneumococci, especially those isolated from nasopharynx, is problematic due to the discrepant results obtained by the conventional identification methods. Several gene technological methods based on the amplification of genes encoding pneumococcal virulence factors, such as pneumolysin (ply) and autolysin, have been used as additional identification methods. Recent studies have shown that especially the ply gene is frequently also present in nonpneumococcal alpha-hemolytic streptococci. In this study, we compared the commonly used phenotypic identification methods with nucleic acid-based methods, commercial AccuProbetrade mark, conventional pneumolysin polymerase chain reaction (Ply-PCR), and real-time Ply-PCR in the identification of alpha-hemolytic streptococcal strains isolated from 100 consecutive nasopharyngeal specimens. We also studied if melting curve analysis and sequencing of the amplification products of a ply gene fragment could be helpful in the identification. Our results suggest that the ply gene present in alpha-hemolytic streptococci differs from that present in pneumococcus, and that melting curve analysis would prove useful in the differentiation of these bacteria.

Association of clinical signs and symptoms with bacterial findings in acute otitis media.

In acute otitis media (AOM), a means of prediction of the bacterial pathogen based on symptoms and signs would be valuable in selecting appropriate antimicrobial treatment. Children in the control arm (n=831) in the Finnish Otitis Media Vaccine Trial were prospectively observed in a study clinic setting from the age of 2 to 24 months. In patients with AOM, myringotomy with aspiration was performed, and middle ear fluid samples were cultured for bacterial pathogens. Symptoms and signs of respiratory infections were thoroughly recorded. Streptococcus pneumoniae, Moraxella catarrhalis, and Haemophilus influenzae were the most common bacterial pathogens. Pneumococcal AOM was associated with more-severe AOM characterized by fever and earache. AOM due to H. influenzae was associated with eye symptoms and findings. Accurate prediction of a bacterial cause of infection based on symptoms and signs of AOM was not possible, but a specific cause was predicted in some situations, with a high probability of applicability to clinical practice.

Prevention of otitis media by adenoidectomy in children younger than 2 years.

OBJECTIVES: To test the effect of adenoidectomy in connection with tympanostomy compared with tympanostomy only in preventing otitis media in children younger than 2 years. DESIGN: Prospective trial with randomized and nonrandomized arms. SETTING: Primary care study clinics. PARTICIPANTS AND INTERVENTIONS: The study participants were selected from 2497 children who had been enrolled in the Finnish Otitis Media Vaccine Trial at the age of 2 months. A total of 306 children, aged 1 to 2 years, who had experienced recurrent episodes of otitis media were randomized into 2 treatment groups: tympanostomy with or without adenoidectomy. Of the 306 children, 137 were operated on according to random basis (randomized trial). The 169 children whose parents declined participation in the randomized trial were operated on according to the parents' preferences (nonrandomized trial). All children were followed up until 2 years of age. The mean follow-up time was 7 months. MAIN OUTCOME MEASURE: The rate of acute otitis media episodes. RESULTS: The average reduction in the rate of all acute otitis media episodes in the adenoidectomy group was 19% (95% confidence interval [CI], -14% to 43%) among children enrolled in the randomized trial and 25% (95% CI, -13% to 50%) in the nonrandomized trial. The reduction in the randomized trial was mainly due to reduction in the rate of pneumococcal otitis media (58%, 95% CI, 16%-79%). CONCLUSION: In children younger than 2 years, concurrent adenoidectomy during the insertion of tympanostomy tubes does not seem to have a major advantage over the insertion of tympanostomy tubes alone in preventing otitis media.

Epidemiological evidence for serotype-independent acquired immunity to pneumococcal carriage.

BACKGROUND: Asymptomatic nasopharyngeal carriage is the main reservoir for transmission of Streptococcus pneumoniae. The rate of both carriage and pneumococcal disease decreases with age. To what extent these changes are the result of developing natural immunity is currently a subject of debate. OBJECTIVE: To study the hypothesis that previous carriage induces serotype-independent protective immunity to new colonization. METHODS: We compared the rates of pneumococcal acquisition for children with different previous carriage histories. We identified 435 episodes of carriage during the first year of life in follow-up data for 99 Bangladeshi children. Cox regression analysis was adjusted for serotype-specific exposure within the family and other confounding factors. RESULTS: Previous pneumococcal carriage was associated with serotype-independent protection from subsequent acquisition (hazard ratio, 0.60 [95% confidence interval, 0.39-0.90]), whereas recent serotype-specific exposure within the family was associated with an 8-fold increase in the rate of acquisition for that serotype. CONCLUSION: Our findings are consistent with the hypothesis that serotype-independent protective immunity is stimulated in young children by previous pneumococcal carriage and reduces the rate of new colonization. This immunity has the potential to modulate the development of carriage, irrespective of the colonizing serotype, and to do so starting early in infancy.

International Circumpolar Surveillance System for invasive pneumococcal disease, 1999-2005.

The International Circumpolar Surveillance System is a population-based surveillance network for invasive bacterial disease in the Arctic. The 7-valent pneumococcal conjugate vaccine (PCV7) was introduced for routine infant vaccination in Alaska (2001), northern Canada (2002-2006), and Norway (2006). Data for invasive pneumococcal disease (IPD) were analyzed to identify clinical findings, disease rates, serotype distribution, and antimicrobial drug susceptibility; 11,244 IPD cases were reported. Pneumonia and bacteremia were common clinical findings. Rates of IPD among indigenous persons in Alaska and northern Canada were 43 and 38 cases per 100,000 population, respectively. Rates in children <2 years of age ranged from 21 to 153 cases per 100,000 population. In Alaska and northern Canada, IPD rates in children <2 years of age caused by PCV7 serotypes decreased by >80% after routine vaccination. IPD rates are high among indigenous persons and children in Arctic countries. After vaccine introduction, IPD caused by non-PCV7 serotypes increased in Alaska.

Serious community-acquired paediatric infections in rural Asia (Bohol Island, Philippines): bacterial meningitis in children less than 5 years of age.

This paper describes the clinical profile and aetiology of bacterial meningitis in infants and children less than 5 y old admitted to a rural general hospital in the Philippines. A total of 989 infants and children 0-59 months old with suspected meningitis using a standardized guideline based on clinical signs and symptoms were prospectively enrolled from April 1994 to May 2000. Blood and CSF were drawn on admission for culture, antigen testing and cell count. All had blood cultures and 623 (63%) had CSF samples. Bacterial aetiology was found in 54 (5%). The most common bacterial pathogens were H. influenzae type b (Hib) (20, 37%) and S. pneumoniae (Pnc) (10, 18%). All of the Hib infections and 8 (80%) Pnc infections were in infants less than 1 y old. 12 (22%) of the subjects with bacterial meningitis died. All strains of S. pneumoniae and H. influenzae were sensitive to chloramphenicol, cotrimoxazole and ampicillin. In conclusion, S. pneumoniae and H. influenzae type b are the most common aetiological agents of bacterial meningitis in a rural area in the Philippines, and occur especially in infants less than 1 y old. Aetiological agents were susceptible to the currently recommended antimicrobial agents.

Is there any specific association between respiratory viruses and bacteria in acute otitis media of young children?

BACKGROUND: Respiratory viral infections are usually preceding or coinciding with acute otitis media (AOM) in children. It is not known if a given viral infection would facilitate invasion of bacterial pathogens into the middle ear in a species-specific way. We reanalysed the microbiological results of the two prospective Finnish Otitis Media (FinOM) studies for this purpose. METHODS: The children had been followed from 2 months to 2 years of age in specific study clinics and all referred AOM events were analysed. Combined results of virus detection tests from middle ear fluid and nasopharyngeal aspirate and those of bacterial culture from middle ear fluid were cross-tabulated for 529 AOM events in the FinOM Cohort Study and for 364 events in the FinOM Vaccine Trial. RESULTS: In both studies the main bacterial pathogens were Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis while the main viruses detected were rhinoviruses and respiratory syncytial virus (plus enteroviruses in the Vaccine Trial). No distinct species-specific associations were observed between the viral and bacterial findings. CONCLUSION: We did not find support to the theory that respiratory infection caused by a given viral species would favour growth of a certain bacterial pathogen in the MEF more than another.

Using multilocus sequence data to define the pneumococcus.

We investigated the genetic relationships between serotypeable pneumococci and nonserotypeable presumptive pneumococci using multilocus sequence typing (MLST) and partial sequencing of the pneumolysin gene (ply). Among 121 nonserotypeable presumptive pneumococci from Finland, we identified isolates of three classes: those with sequence types (STs) identical to those of serotypeable pneumococci, suggesting authentic pneumococci in which capsular expression had been downregulated or lost; isolates that clustered among serotypeable pneumococci on a tree based on the concatenated sequences of the MLST loci but which had STs that differed from those of serotypeable pneumococci in the MLST database; and a more diverse collection of isolates that did not cluster with serotypeable pneumococci. The latter isolates typically had sequences at all seven MLST loci that were 5 to 10% divergent from those of authentic pneumococci and also had distinct and divergent ply alleles. These isolates are proposed to be distinct from pneumococci but cannot be resolved from them by optochin susceptibility, bile solubility, or the presence of the ply gene. Complete resolution of pneumococci from the related but distinct population is problematic, as recombination between them was evident, and a few isolates of each population possessed alleles at one or occasionally more MLST loci from the other population. However, a tree based on the concatenated sequences of the MLST loci in most cases unambiguously distinguished whether a nonserotypeable isolate was or was not a pneumococcus, and the sequence of the ply gene fragment was found to be useful to resolve difficult cases.

Survival of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis frozen in skim milk- tryptone-glucose-glycerol medium.

In STGG (skim milk, tryptone, glucose, glycerol) medium at -80 degrees C, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis isolates survived for at least 3 years, and the same species have survived in nasopharyngeal swabs for at least 1.5 years. At -20 degrees C, S. pneumoniae and M. catarrhalis survived for 1.5 years, but H. influenzae survived for only 2 months.

Ability of pneumococcal serotypes and clones to cause acute otitis media: implications for the prevention of otitis media by conjugate vaccines.

The relative abilities of pneumococcal serotypes and strains (clones) to cause acute otitis media (AOM) were investigated by comparing the serotypes and genotypes of pneumococci recovered from cases of AOM (n = 149) in children <2 years of age with those from nasopharyngeal carriage (n = 288) in age-matched controls from the same region. The odds ratio (OR) for association of pooled vaccine serotypes with AOM was found to be slightly elevated over unity, although this was not significantly different from that of pooled nonvaccine or vaccine-related serotypes. Comparing individual serotypes, 19F and 23F had 2- to 2.5-fold higher ORs, although these were not markedly different from the ORs of nonvaccine serotypes. None of the major clones had an OR that was significantly greater than the average, and the differences in ORs among serotypes and clones were much less than those for invasive disease, suggesting little variation in their ability to cause AOM. We conclude that serotype replacement may reduce the long-term efficacy of these vaccines against AOM.