Incidence and severity of respiratory syncytial virus pneumonia in rural Kenyan children identified through hospital surveillance

Abstract

Background: Although necessary for developing a rationale for vaccination, the burden of severe respiratory syncytial virus (RSV) disease in children in resource-poor settings remains poorly defined.

Methods: We conducted prospective surveillance of severe and very severe pneumonia in children aged <5 years admitted from 2002 through 2007 to Kilifi district hospital in coastal Kenya. Nasal specimens were screened for RSV antigen by immunofluorescence. Incidence rates were estimated for the well-defined population.

Results: Of 25,149 hospital admissions, 7359 patients (29%) had severe or very severe pneumonia, of whom 6026 (82%) were enrolled. RSV prevalence was 15% (20% among infants) and 27% during epidemics (32% among infants). The proportion of case patients aged 3 months was 65%, and the proportion aged 6 months was 43%. Average annual hospitalization rates were 293 hospitalizations per 100,000 children aged <5 years (95% confidence interval, 271-371 hospitalizations per 100,000 children aged <5 years) and 1107 hospitalizations per 100,000 infants (95% confidence interval, 1012-1211 hospitalizations per 100,000 infants). Hospital admission rates were double in the region close to the hospital. Few patients with RSV infection had life-threatening clinical features or concurrent serious illnesses, and the associated mortality was 2.2%.

Conclusions: In this low-income setting, rates of hospital admission with RSV-associated pneumonia are substantial; they are comparable to estimates from the United States but considerably underestimate the burden in the full community. An effective vaccine for children aged >2 months (outside the age group of poor responders) could prevent a large portion of RSV disease. Severity data suggest that the justification for RSV vaccination will be based on the prevention of morbidity, not mortality.

Fig. 1

Flow diagram of recruitment and sample testing of children aged under 5 years (left) and infants (right) admitted to Kilifi District Hospital from January 2002 to December 2007. ‘Tested’ children refers to those who were enrolled, had a sample collected and tested, with the remainder either not enrolled or enrolled and a sample not taken and tested. Percentages in brackets within a box refer to the proportion of individuals from the preceding box. Note that among those untested who refused participation 121 children aged less than 5 years and 90 infants subsequently died and contribute to the denominator of the case fatality ratio (CFR).

Fig.2

Geographical variation within the Kilifi Health and Demographic Surveillance System in the incidence of RSV associated severe or very severe pneumonia in under 5 year old admissions to Kilifi District Hospital (KDH). Represented is the rate of hospitalization (per 100,000 per year) for the 5 year period May 2002 to April 2007, categorised into 4 levels and stratified by administrative sub-location. Main roads, Kilifi Creek (C), and KDH (H), are identified. The zone marked by a white perimeter has a 5km radius from its central point, KDH.