Pneumococcal capsular antigen detection after enrichment culture: an alternative to culture methods in epidemiologic research

Superiority of trans-oral over trans-nasal sampling in detecting Streptococcus pneumoniae colonization in adults

The human nasopharynx is the main reservoir for Streptococcus pneumoniae. We applied conventional and molecular methods to determine the prevalence of S. pneumoniae nasopharyngeal colonization in adults. Paired trans-orally and trans-nasally obtained nasopharyngeal samples from 268 parents of 24-month-old children were assessed for pneumococcal presence. Parents were classified as colonized when live pneumococci were recovered from either sample cultured on medium selective for S. pneumoniae. Of the 52 (19%) colonized parents 49 (18%) were culture-positive in trans-nasal and 10 (4%) in trans-oral samples. Bacterial growth was harvested from these cultures, DNA isolated and tested by quantitative-PCR (qPCR) targeting lytA and piaA genes specific for S. pneumoniae. A sample was considered positive if signals for both genes were detected. Altogether 105 (39%) individuals were classified as positive for pneumococcus by qPCR including 50 (19%) in trans-nasal and 94 (35%) in trans-oral settings. Although significantly more trans-nasal compared to trans-oral samples were culture-positive for S. pneumoniae at the primary diagnostic step (p<0.001) the opposite was observed in qPCR results (p<0.001). To confirm the presence of live pneumococcus in samples positive by qPCR but negative at the initial diagnostic step, we serially-diluted cell harvests, re-cultured and carefully examined for S. pneumoniae presence. Live pneumococci were recovered from an additional 43 parents including 42 positive in trans-oral and 4 in trans-nasal samples increasing the number of individuals culture- and qPCR-positive to 93 (35%) and positive by either of two methods to 107 (40%). There were significantly more trans-oral than trans-nasal samples positive for pneumococcus by both culture and qPCR (n = 71; 27%; vs. n = 50; 19%; p<0.05). Our data suggest that pneumococcal colonization is more common in adults than previously estimated and point towards the superiority of a trans-oral over a trans-nasal approach when testing adults for colonization with S. pneumoniae.

Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis

BACKGROUND

The global burden of disease attributable to seasonal influenza virus in children is unknown. We aimed to estimate the global incidence of and mortality from lower respiratory infections associated with influenza in children younger than 5 years.

METHODS

We estimated the incidence of influenza episodes, influenza-associated acute lower respiratory infections (ALRI), and influenza-associated severe ALRI in children younger than 5 years, stratified by age, with data from a systematic review of studies published between Jan 1, 1995, and Oct 31, 2010, and 16 unpublished population-based studies. We applied these incidence estimates to global population estimates for 2008 to calculate estimates for that year. We estimated possible bounds for influenza-associated ALRI mortality by combining incidence estimates with case fatality ratios from hospital-based reports and identifying studies with population-based data for influenza seasonality and monthly ALRI mortality.

FINDINGS

We identified 43 suitable studies, with data for around 8 million children. We estimated that, in 2008, 90 million (95% CI 49-162 million) new cases of influenza (data from nine studies), 20 million (13-32 million) cases of influenza-associated ALRI (13% of all cases of paediatric ALRI; data from six studies), and 1 million (1-2 million) cases of influenza-associated severe ALRI (7% of cases of all severe paediatric ALRI; data from 39 studies) occurred worldwide in children younger than 5 years. We estimated there were 28,000-111,500 deaths in children younger than 5 years attributable to influenza-associated ALRI in 2008, with 99% of these deaths occurring in developing countries. Incidence and mortality varied substantially from year to year in any one setting.

INTERPRETATION

Influenza is a common pathogen identified in children with ALRI and results in a substantial burden on health services worldwide. Sufficient data to precisely estimate the role of influenza in childhood mortality from ALRI are not available.

FUNDING

WHO; Bill & Melinda Gates Foundation.

Phenotypic and genotypic characterization of Streptococcus pneumoniae strains colonizing children attending day-care centers in Norway

A cross-sectional study of nasopharyngeal colonization with Streptococcus pneumoniae was performed among 573 children attending 29 day-care centers (DCCs) in Norway prior to the start of mass vaccination with the heptavalent pneumococcal conjugate vaccine (PCV-7). A sensitive sampling method was employed, including transport in an enrichment broth and serotyping of pneumococci directly from the broth, in addition to traditional single-colony isolation from blood agar plates. The prevalence of carriage was high, peaking at 88.7% in 2-year-olds. More than one serotype was isolated from 12.7% of the carriers. Of 509 isolates obtained, 227 (44.6%) belonged to the PCV-7 serotypes. Penicillin nonsusceptibility was rare (1.8% of the isolates). Nonsusceptibility to erythromycin (5.9%), clindamycin (2.0%), and tetracycline (5.5%) was associated with PCV-7 serotypes (P < 0.001). Multilocus sequence typing was performed on the whole strain collection, revealing 102 sequence types (STs), of which 31 (30.4%) were novel. Eleven isolates (2.2%) belonged to the England(14)-9 clone, and 19 isolates (3.7%) belonged to, or were single-locus variants of, the Portugal(19F)-21 clone. The pneumococcal populations within the DCCs were composed of a majority of isolates with STs shared between the DCCs and a minority of isolates with STs unique for each DCC. The highest numbers of different STs, including novel STs, were found within the most frequent serotypes. Our study indicates that carriage of S. pneumoniae is highly prevalent among children in Norwegian DCCs, with a genetically diverse pneumococcal population consisting of unique microepidemic DCC populations.

A cross-sectional survey of the prevalence of Streptococcus pneumoniae nasopharyngeal carriage in Belgian infants attending day care centres

Nasopharyngeal carriage is a major factor in the transmission of pneumococcal disease. The aim of this study was to determine the prevalence of asymptomatic nasopharyngeal carriage of Streptococcus pneumoniae and the distribution of serogroups and serotypes in children aged 3-36 months attending day care centres in Belgium. A single nasopharyngeal swab was cultured from 467 children attending 30 different day care centres between December 2000 and March 2001. S. pneumoniae isolates were serotyped and their antibiotic susceptibilities assessed by disk diffusion. The overall nasopharyngeal carriage rate for S. pneumoniae was 21% in the 467 children. None of the commonly accepted risk factors studied was associated significantly with carriage. Capsular serotypes isolated were 19F (27.3%), 6B (20.2%), 23F (19.2%), 19A (10.1%), 6A (7.1%), 14 (5.1%) and others (11.0%). Theoretical coverage by the seven-valent (serotypes 4, 6B, 9V, 14, 18C, 19F and 23F) pneumococcal conjugate vaccine was 73.7%. Fourteen (14.1%) of 99 strains were non-susceptible to penicillin, 48 (48.5%) to tetracycline and 61 (61.6%) to erythromycin. Theoretical coverage by the seven-valent pneumococcal conjugate vaccine was 93% for the penicillin-resistant serotypes, 69% for the tetracycline-resistant serotypes and 75% for the erythromycin-resistant serotypes. Use of the seven-valent pneumococcal conjugate vaccine could potentially reduce nasopharyngeal carriage of the antibiotic-resistant strains.

Type-specific enzyme immunoassay for detection of pneumococcal capsular polysaccharide antigens in nasopharyngeal specimens

We developed a new competitive EIA method for the demonstration of pneumococcal capsular polysaccharides from respiratory samples. The pediatric types 4, 6B, 9V, 14, 18C, 19F and 23F were selected for this study, because these capsular polysaccharides were included in the first heptavalent pneumococcal conjugate vaccines, which were used in the Finnish Otitis Media Vaccine Trial. Sensitivity of the EIA tests for purified polysaccharide antigens varied between 5 and 100 ng/ml, depending on the type. The assays performed well in 100 nasopharyngeal samples (NPS) samples processed through an enrichment culture, with an almost 100% sensitivity compared with routine culture. The method appeared type-specific, except that EIA for 6B capsule also detected 6A. The method is applicable for type-specific identification of pneumococcus in carriage studies.

Report from a WHO Working Group: standard method for detecting upper respiratory carriage of Streptococcus pneumoniae

BACKGROUND

Numerous studies evaluating the efficacy of conjugate pneumococcal vaccines are being conducted or planned throughout the world. Some of these studies are evaluating the effect of vaccine on nasopharyngeal (NP) carriage.

METHODS

The World Health Organization established a Working Group comprised of representatives from these trials and other NP colonization experts to establish core, standardized methods for the study of pneumococcal NP colonization that could be used in these trials. The intent was to reduce or eliminate variability in key methods which themselves could contribute to variability of observed pneumococcal NP colonization. In this way variability of vaccine effects between trials on NP colonization could more easily be analyzed for population or vaccine differences without the confounding effect caused by differences in study methodology.

RESULTS

This paper presents the evidence base supporting the need for standardized NP colonization study methods, the methods themselves (Core Consensus Methods), including collection techniques, culture media, equipment, serotyping, storage of specimens and transport of isolates agreed on by the Working Group as well as a discussion of research priorities.

CONCLUSIONS

The Core Consensus Methods provide a common methodology to conduct pneumococcal NP colonization studies with minimum interstudy method variability. The intention is to allow more meaningful comparisons of study results from conjugate pneumococcal vaccine trials.

Report from a WHO working group: standard method for detecting upper respiratory carriage of Streptococcus pneumoniae

BACKGROUND

Numerous studies evaluating the efficacy of conjugate pneumococcal vaccines are being conducted or planned throughout the world. Some of these studies are evaluating the effect of vaccine on nasopharyngeal (NP) carriage.

METHODS

The World Health Organization established a Working Group composed of representatives from these trials and other NP colonization experts to establish core, standardized methods for the study of pneumococcal NP colonization that could be used in these trials. The intent was to reduce or eliminate variability in key methods which themselves could contribute to variability of observed pneumococcal NP colonization. In this way variability of vaccine effects between trials on NP colonization could more easily be analyzed for population or vaccine differences without the confounding effect caused by differences in study methodology.

RESULTS

This paper presents the evidence base supporting the need for standardized NP colonization study methods, the methods themselves (Core Consensus Methods found in the electronic version of this article at www.pidj.com and on the WHO website at http://www.who.int/vaccines-research/rd/docsrd.shtml), including collection techniques, culture media, equipment, serotyping, storage of specimens and transport of isolates agreed on by the Working Group as well as a discussion of research priorities.

CONCLUSIONS

The Core Consensus Methods provide a common methodology to conduct pneumococcal NP colonization studies with minimum interstudy method variability. The intention is to allow more meaningful comparisons of study results from conjugate pneumococcal vaccine trials.

Pneumococcal carriage in children during their first two years: important role of family exposure

BACKGROUND

Close family and day-care contacts have been identified as risk factors for pneumococcal (Pnc) carriage. This study addresses the risk of Pnc carriage by infants 2 to 24 months of age in terms of simultaneous carriage of pneumococcus by family members.

METHODS

Nasopharyngeal swabs were collected from 100 Finnish infants and their family members on 10 scheduled visits (when infant was 2, 3, 4, 5, 6, 9, 12, 15, 18 and 24 months of age). The 7 most common pneumococcal serogroups (4, 6, 9, 14, 18, 19, 23), also represented in the new heptavalent Pnc conjugate vaccine, were analyzed. Marginal logistic regression analyses were performed to assess the relative importance of different predictors for carriage.

RESULTS

The carriage of the studied Pnc serogroups increased with age, being highest at the age of 18 months (28%). Among children older than 6 months of age, the strongest predictor of carriage was simultaneous carriage of the same serogroup by another family member (odds ratio, 3.8; 95% confidence interval, 2.1 to 6.9). At the age of 6 months or younger, carriage was rare and was not significantly associated with a family carriage.

CONCLUSIONS

Young infants (< or =6 months old) were largely protected from pneumococcal carriage. After this age family transmission seemed very important despite the small family size. Contrary to some earlier studies communal day care was not associated with an increased risk of Pnc carriage. This could be partly because of the long parental leave in Finland and thus the late age of starting organized day care.

Defining the burden of pneumonia in children preventable by vaccination against Haemophilus influenzae type b

OBJECTIVES

To determine the burden of pneumonia requiring hospitalization in infants and young children preventable by vaccination against Haemophilus influenzae type b (Hib).

DESIGN

Vaccination centers in Santiago, Chile, were randomly selected to administer PRP-T, an Hib conjugate vaccine, combined with diphtheria-tetanus toxoids-pertussis (DTP) vaccine or DTP alone.

SUBJECTS

Infants who received > or =2 doses of DTP or DTP and Hib conjugate vaccine combined.

MAIN OUTCOME MEASURES

Pneumonia episodes leading to hospitalization accompanied by indicators of likely bacterial infection including radiologic evidence of alveolar consolidation or pleural effusion, an elevated erythrocyte sedimentation rate (> or =40 mm/h) or bronchial breath sounds on auscultation.

RESULTS

In participants age 4 to 23 months, PRP-T reduced the incidence of pneumonia associated with alveolar consolidation or pleural effusion by 22% (95% confidence interval, -7 to 43) from 5.0 to 3.9 episodes per 1000 children per year. When the pneumonia case definition included any of the following, alveolar consolidation, pleural effusion, erythrocyte sedimentation rate > or =40 mm/h or bronchial breath sounds, PRP-T provided 26% protection (95% confidence interval, 7 to 44) and prevented 2.5 episodes per 1000 children per year.

CONCLUSIONS

Hib vaccine provides substantial protection against nonbacteremic pneumonia, particularly those cases with alveolar consolidation, pleural effusion or other signs of likely bacterial infection. Hib vaccination prevented approximately 5 times as many nonbacteremic pneumonia cases in infants as meningitis cases, thus indicating that the largest part of the effect of Hib vaccination might be undetectable by routine culture methods.