Abstract
BackgroundStreptococcus pneumoniae is an important cause of community acquired pneumonia, sepsis, meningitis and otitis media globally and has been incriminated as a major cause of serious childhood bacterial infections in The Gambia. Better understanding of the dynamics of transmission and carriage will inform control strategies.MethodsThis study was conducted among 196 mother-infant pairs recruited at birth from six villages in the West Kiang region of The Gambia. Nasopharyngeal swabs were collected from mother-infant pairs at birth (within 12 hours of delivery), 2, 5 and 12 months. Standard techniques of culture were used to identify carriage and serotype S. pneumoniae.ResultsOf 46 serotypes identified, the 6 most common, 6A, 6B, 14, 15, 19F and 23F, accounted for 67.3% of the isolates from infants. Carriage of any serotype among infants rose from 1.5% at birth to plateau at approximately 80% by 2 m (prevalence at 2 m = 77%; 5 m = 86%; 12 m = 78%). Likewise, maternal carriage almost doubled in the first 2 months post-partum and remained elevated for the next 10 m (prevalence at birth = 13%; 2 m = 24%; 5 m = 22%; 12 m = 21%). Carriage was significantly seasonal in both infants and mothers with a peak in December and lowest transmission in August. The total number of different serotypes we isolated from each infant varied and less than would be expected had the serotypes assorted independently. In contrast, this variability was much as expected among mothers. The half-life of a serotype colony was estimated to be 1.90 m (CI95%: 1.66-2.21) in infants and 0.75 m (CI95%: 0.55-1.19) in mothers. While the odds for a serotype to be isolated from an infant increased by 9-fold if it had also been isolated from the mother, the population attributable fraction (PAF) of pneumococcal carriage in infants due to maternal carriage was only 9.5%. Some marked differences in dynamics were observed between vaccine and non-vaccine serotypes.ConclusionsColonisation of the nasopharynx in Gambian infants by S. pneumoniae is rapid and highly dynamic. Immunity or inter-serotype competition may play a role in the dynamics. Reducing mother-infant transmission would have a minimal effect on infant carriage.
Highlights
Streptococcus pneumoniae is an important cause of community acquired pneumonia, sepsis, meningitis and otitis media globally and has been incriminated as a major cause of serious childhood bacterial infections in The Gambia
2.6 million preschool children die from pneumonia annually in developing countries, and almost half of these deaths are attributable to S. pneumoniae either exclusively or in conjunction with viral infections and/or malnutrition [2,3,4,5]
Our findings provide baseline information on the dynamics of carriage that we hope will prove useful in the preparation for the introduction and evaluation of the 13-valent conjugate pneumococcal carriage in The Gambia and, more generally, in understanding the transmission of the infection in infancy
Summary
Streptococcus pneumoniae is an important cause of community acquired pneumonia, sepsis, meningitis and otitis media globally and has been incriminated as a major cause of serious childhood bacterial infections in The Gambia. Streptococcus pneumoniae is a leading cause of invasive bacterial meningitis, acute respiratory infections and pneumonia among infants and children less than two years in developing countries [1]. Nasopharyngeal carriage of S. pneumoniae is a risk factor for the development of respiratory diseases and pneumonia [6,7,8]. The relationship between carriage and disease is not well understood, evidence suggests that local or systemic invasive infection is caused by serotypes that bind to the epithelial surface of the respiratory tract [9,10,11]. Nasopharyngeal carriage is the source of pneumococcal spread to other individuals mainly in intimate and overcrowded conditions. Over 80% of apparently healthy Gambian infants are nasopharyngeal pneumococcal carriers [14,15]. Carriage is relatively high (50%) among Gambian adults [15]
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