Factors associated with increased risk of progression to respiratory syncytial virus-associated pneumonia in young Kenyan children.

Emelda A Okiro,Mwanajuma Ngama,Patricia A Cane,Graham F Medley,D James Nokes,Ann Bett

doi:10.1111/j.1365-3156.2008.02092.x

Abstract

ObjectivesTo identify factors associated with developing severe respiratory syncytial virus (RSV) pneumonia and their commonality with all-cause lower respiratory tract infection (LRTI), in order to isolate those risk factors specifically associated with RSV-LRTI and identify targets for control.MethodsA birth cohort of rural Kenyan children was intensively monitored for acute respiratory infection (ARI) over three RSV epidemics. RSV was diagnosed by immunofluorescence of nasal washings collected at each ARI episode. Cox regression was used to determine the relative risk of disease for a range of co-factors.ResultsA total of 469 children provided 937 years of follow-up, and experienced 857 all-cause LRTI, 362 RSV-ARI and 92 RSV-LRTI episodes. Factors associated with RSV-LRTI, but not RSV-ARI, were severe stunting (z-score ≤−2, RR 1.7 95%CI 1.1–2.8), crowding (increased number of children, RR 2.6, 1.0–6.5) and number of siblings under 6 years (RR 2.0, 1.2–3.4). Moderate and severe stunting (z-score ≤−1), crowding and a sibling aged over 5 years sleeping in the same room as the index child were associated with increased risk of all-cause LRTI, whereas higher educational level of the primary caretaker was associated with protection.ConclusionWe identify factors related to host nutritional status (stunting) and contact intensity (crowding, siblings) which are distinguishable in their association with RSV severe disease in infant and young child. These factors are broadly in common with those associated with all-cause LRTI. The results support targeted strategies for prevention.

Highlights

Pneumonia is the leading cause of morbidity and mortality in the developing world (Bryce et al 2005; WHO 2006a; Greenwood et al 2007) and respiratory viruses make a major contribution to this disease burden (Selwyn 1990; Monto 2002)
The risk factors for RSV-associated disease may be common to all pneumonias, specific to viral pneumonias or may be agentspecific
Past studies report a number of possible risk factors for increased viral disease severity, most of which are common to RSV

Summary

Introduction

Pneumonia is the leading cause of morbidity and mortality in the developing world (Bryce et al 2005; WHO 2006a; Greenwood et al 2007) and respiratory viruses make a major contribution to this disease burden (Selwyn 1990; Monto 2002). Past studies report a number of possible risk factors for increased viral disease severity, most of which are common to RSV These may be environmental [higher household population density (Aaby 1988; Weber et al 1999; Suwanjutha et al 2002), attending school (Monto & Sook 1971; Hall et al 1976), increased smoke exposure (Gardner et al 1984; Cruz et al 1990)], host factors [e.g. born prematurely (Nielsen et al 2003), genetic susceptibility (Karron et al 1999), poor nutritional status (Vardas et al 1999; Loscertales et al 2002; Djelantik et al 2003)] and pathogen (Mufson et al 1988; Sullender 2000) specific factors. Severe RSV in developing countries has been a 2008 Blackwell Publishing Ltd

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