A Decline in the Incidence of Invasive Non-Typhoidal Salmonella Infection in the Gambia Temporally Associated with a Decline in Malaria Infection

Grant Mackenzie,Philip C Hill,Michael Walther,Tumani Corrah,David C W Mabey,Serign J Ceesay,Umberto D'Alessandro,Kalifa A Bojang,Brian M Greenwood,Usman N A Ikumapayi,Tim O'Dempsey,Judith Satoguina,Godwin Enwere,David J Conway,Debasish Saha,Richard A Adegbola,David Joseph Diemert

doi:10.1371/journal.pone.0010568

Abstract

BackgroundMalaria is a risk factor for invasive non-typhoidal Salmonella (NTS) infection in children. In the last 10 years, indices of malaria infection in The Gambia have fallen substantially.MethodsWe compared temporal trends of childhood malaria and NTS infection in two Gambian locations. In Fajara, on the coast, the incidence of NTS infection at three time points between 1979 and 2005 was compared to the percentage of malaria positive outpatient thick blood films and the percentage of admissions associated with malaria over time. In Basse, in the eastern part of the country, the incidence of NTS infection at three time points between 1989 and 2008 was compared to the prevalence of malaria parasitaemia at four time points between 1992 and 2008.ResultsThe estimated incidence of NTS infection in Fajara fell from 60 (1979–1984) to 10 (2003–05) cases per 100,000 person years. The proportion of outpatients in Fajara with suspected malaria who were parasitaemic fell from 33% (1999) to 6% (2007) while the proportion of admissions associated with malaria fell from 14.5% (1999) to 5% (2007). In Basse, the estimated incidence of NTS infection fell from 105 (1989–1991) to 29 (2008) cases per 100,000 person years while the prevalence of malaria parasitaemia fell from 45% (1992) to 10% (2008). The incidence of pneumococcal bacteraemia in Fajara and Basse did not fall over the study period.ConclusionsThese data support an association between malaria and NTS infection. Reductions in malaria infection may be associated with reduced rates of invasive childhood NTS infection.

Highlights

Non-typhoidal Salmonella species (NTS) are a leading cause of invasive bacterial infection in African children and are responsible for many deaths [1,2]
Fajara Over a 69 month period from 1979 until 1984, pathogenic bacteria were isolated from 259 patients less than 5 years of age who presented to the Medical Research Council (MRC) Hospital, Fajara; 69 were non-typhoidal Salmonella (NTS) and 38 were pneumococci (NTS:P = 1.8) [4] (Table 2)
During 32 months of a Haemophilus influenzae type b (Hib) conjugate vaccine trial (1993–95), 2408 blood cultures were taken and 39 Salmonella spp. and 76 pneumococci were isolated from blood (NTS:P = 0.51) [12]

Summary

Introduction

Non-typhoidal Salmonella species (NTS) are a leading cause of invasive bacterial infection in African children and are responsible for many deaths [1,2]. Evidence suggests that malaria is a risk factor for invasive NTS infection in children. If malaria is a risk factor for NTS infection, it would be anticipated that a fall in malaria incidence would be associated with reduced rates of NTS infection. To investigate this hypothesis we reviewed data on malaria and NTS infection in two regions of The Gambia collected during the past 30 years. Malaria is a risk factor for invasive non-typhoidal Salmonella (NTS) infection in children. In the last 10 years, indices of malaria infection in The Gambia have fallen substantially

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Conclusion