Transmission of Streptococcus pneumoniae in an urban slum community☆
Introduction
Streptococcus pneumoniae is a major cause of severe infections such as meningitis, septicemia and pneumonia worldwide. Risk groups for invasive pneumococcal disease are young children under the age of 2 years, elderly people, and immunocompromised patients.1 Nasopharyngeal carriage of pneumococci is likely to occur in all individuals at least once during infancy.2 Infants are an important reservoir for community-wide transmission, which for the most part produces asymptomatic carriage.3 Invasive pneumococcal disease is a relatively rare outcome and originates from colonization with a homologous strain.4 Although a genetically diverse population of pneumococcal clones is found in carriage, a limited number of clones appear to produce invasive disease.5, 6 To distinguish between clones that are capable of producing carriage or invasive disease, both clinical and nasopharyngeal isolates from the same geographic region and time period need to be characterized.
Several studies have compared carriage and invasive disease isolates from the same epidemiological setting.5, 6, 7, 8 A study performed in Oxford, England found that clones with the same serotype had similar invasive potential indicating that serotype may be more important than genotype in the ability of pneumococci to cause invasive disease.7 In contrast, a study from Sweden identified clones that belonged to the same serotype but had different abilities to cause invasive disease. In addition, this study found that clones with different serotypes, which were presumably generated due to capsular switch phenomenon, had the same disease potential.8
At present, 1 billion of the world's population resides in urban slums, most of which are situated in developing countries.9 Much of this marginalized population has not benefited from the advances in prevention afforded by immunization with pneumococcal protein-capsular conjugate vaccines.10 Although underlying conditions of poverty presumably lead to high rates of pneumococci carriage and invasive disease, little information is available with respect to disease burden and transmission of S. pneumoniae within these communities. Salvador is the third largest city in Brazil (population, 2.8 million inhabitants) in which more than 60% of the population resides in slum settlements. Active surveillance in Salvador found that the annual incidence for pneumococcal meningitis was 31.7 and 8 cases per 100,000 person-years in children under one and five years of age, respectively.11 The large majority (>80%) of meningitis cases in the city were residents of slum communities (favelas). Children <2 years had a significantly increased risk of acquiring penicillin-nonsusceptible (PNSP) isolates than children >2 years. Furthermore, 50% of all the PNSP meningitis cases were caused by a single serotype 14 clone, which has disseminated throughout Brazil.11, 12 We herein report the findings of a cross-sectional study conducted in a slum community in Salvador, where on-going surveillance for pneumococcal meningitis has been conducted, to identify the prevalence and risk factors for S. pneumoniae nasopharyngeal carriage among community residents. Furthermore, genotyping methods were used to determine the contribution of clones in the transmission of S. pneumoniae within households and the community.
Section snippets
Study site and population
The survey was carried out in the slum community (favela) of Nordeste de Amaralina in the city of Salvador, Brazil between July 2000 and May 2001. According to the national census bureau,13 60% of the 2.6 million inhabitants of Salvador resides in slums such as Nordeste de Amaralina. In 2000, the study community had a population of 23,980 inhabitants, distributed within 18 census district in an area of 0.5 km2.14 A representative census district was selected as the study within this community.
Prevalence and risk factors for S. pneumoniae carriage among slum residents
We identified 282 eligible subjects during visits of 39 households. The mean number of inhabitants per households was 7 (range: 3–14). Mean monthly per capita household income was US$ 73.00 (inter-quartile range, 39.8–98.4). Among 282 eligible subjects, 262 (93%) were enrolled for the survey, of which 57% were female and median age was 16 years. Among the 39 study households, 14 (36%) and 31 (79%) had at least one child <2 and <5 years, respectively.
The prevalence of S. pneumoniae
Discussion
This prevalence study performed in an urban slum community in Brazil found that 36% of the residents were carriers of S. pneumoniae. Pneumococcal carriage rates vary significantly depending on the geographic region and underlying socio-economic conditions.20, 21, 22 However, in this study, the high prevalence of pneumococcal carriage among children <5 years old (65%) was similar to those reported in developing countries.23, 24, 25 School attendance was found to be an independent predictor for
Conflict of interest
The authors do not have any commercial or other association that might pose a conflict of interest with respect to the study, except for M.M. and M.A.B who are employees of Novartis Vaccines.
Acknowledgments
We thank the families of the study community which participated in the study. We also thank laboratory assistants Cíntia Carla, Adriano Queiroz and Maviany Mota, for their immensurable help; Richard Facklam for advice during laboratory analysis and confirmation of the serotyping results. This work was supported by grants from the Oswaldo Cruz Foundation, Brazilian Ministry of Health (0250.250.415); the Brazilian National Research Council (300.861/96-6, 521.132/98–3 and PRONEX 4196086200); the
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