Abstract
BackgroundWe conducted an ancillary study among individuals who had participated in a PCV-7 trial in rural Gambia, to determine the influence of season on the prevalence of pneumococcal carriage.Methods636 individuals above 30 months of age were followed from 4 to 20 months after vaccination with PCV-7 or meningococcal-conjugate-vaccine. Nasopharyngeal swabs were collected periodically between November 2006 and June 2008. Overall, 4,495 NPS were collected.ResultsPrevalence of pneumococcal nasopharyngeal carriage in the study subjects (median age 11 years) was 55.0%; this prevalence decreased linearly with increasing age (p = 0.001). Prevalence of carriage was significantly higher during the dry than the rainy season for any pneumococcal carriage [57.6% versus 47.8% (p<0.001)], pneumococcal vaccine serotype carriage [10.3% versus 6.5% (p< 0.001)] and non-vaccine serotype carriage [49.7% versus 42.7% (p<0.001)]. Differences remained significant in the adjusted analysis.ConclusionsIn areas of Africa with marked variation in rainfall, seasonality of pneumococcal carriage needs to be considered when interpreting carriage data.
Highlights
Streptococcus pneumoniae, the pneumococcus, is an important cause of pneumonia, meningitis and febrile bacteraemia [1]
But not all situations, a decrease of both carriage and invasive pneumococcal disease (IPD) due VT has been followed by an increase in carriage and IPD caused by serotypes that were not represented in the vaccine–non-vaccine types (NVT)—a phenomenon called serotype replacement [17,18,19,20]
The primary aim of the analysis reported in this paper has been to determine the impact of season on pneumococcal carriage in The Gambia, a tropical country with two marked annual seasons—a hot dry season which extends from November to May and a shorter rainy between June and October
Summary
Streptococcus pneumoniae, the pneumococcus, is an important cause of pneumonia, meningitis and febrile bacteraemia [1]. In developing countries, including those in sub-Saharan Africa, incidence rates of invasive pneumococcal disease (IPD) are very high, among young children [2,3,4]. In Africa, where rates of IPD are among the highest in the world, the prevalence of carriage is very high among healthy individuals of all age groups, in both rural and peri-urban areas [6,7,8]. Pneumococcal conjugate vaccines (PCVs) reduce IPD due to serotypes included in the vaccine–vaccine types (VT)–among both vaccinated individuals and their contacts (the latter a consequence of the indirect, herd effect of the vaccine) [9,10,11,12]. We conducted an ancillary study among individuals who had participated in a PCV-7 trial in rural Gambia, to determine the influence of season on the prevalence of pneumococcal carriage.
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