A cross-sectional seroepidemiological survey of typhoid fever in Fiji.

Conall H Watson,Ruklanthi De Alwis,Jorge Cano,Kitione Rawalai,Jerimaia Coriakula,Kylie Jenkins,E Kim Mulholland,Nga Tran Vu Thieu,Eric J Nilles,Stephen Baker,Mere Taufa,W John Edmunds,Colleen L Lau,Tan Trinh Van,Niel Hens,Mike Kama,John H Lowry,Dung Tran Thi Ngoc

doi:10.1371/journal.pntd.0005786

Abstract

Fiji, an upper-middle income state in the Pacific Ocean, has experienced an increase in confirmed case notifications of enteric fever caused by Salmonella enterica serovar Typhi (S. Typhi). To characterize the epidemiology of typhoid exposure, we conducted a cross-sectional sero-epidemiological survey measuring IgG against the Vi antigen of S. Typhi to estimate the effect of age, ethnicity, and other variables on seroprevalence. Epidemiologically relevant cut-off titres were established using a mixed model analysis of data from recovering culture-confirmed typhoid cases. We enrolled and assayed plasma of 1787 participants for anti-Vi IgG; 1,531 of these were resident in mainland areas that had not been previously vaccinated against S. Typhi (seropositivity 32.3% (95%CI 28.2 to 36.3%)), 256 were resident on Taveuni island, which had been previously vaccinated (seropositivity 71.5% (95%CI 62.1 to 80.9%)). The seroprevalence on the Fijian mainland is one to two orders of magnitude higher than expected from confirmed case surveillance incidence, suggesting substantial subclinical or otherwise unreported typhoid. We found no significant differences in seropositivity prevalences by ethnicity, which is in contrast to disease surveillance data in which the indigenous iTaukei Fijian population are disproportionately affected. Using multivariable logistic regression, seropositivity was associated with increased age (odds ratio 1.3 (95% CI 1.2 to 1.4) per 10 years), the presence of a pit latrine (OR 1.6, 95%CI 1.1 to 2.3) as opposed to a septic tank or piped sewer, and residence in settlements rather than residential housing or villages (OR 1.6, 95% CI 1.0 to 2.7). Increasing seropositivity with age is suggestive of low-level endemic transmission in Fiji. Improved sanitation where pit latrines are used and addressing potential transmission routes in settlements may reduce exposure to S. Typhi. Widespread unreported infection suggests there may be a role for typhoid vaccination in Fiji, in addition to public health management of cases and outbreaks.

Highlights

Typhoid fever is a systemic disease resulting from infection by the bacterium Salmonella enterica subspecies enterica serovar Typhi
Fiji has experienced a decade-long increase in typhoid fever cases, a potentially life-threatening systemic bacterial disease caused by Salmonella Typhi
We found one in three residents of mainland, unvaccinated Fiji had detectable antibody against Vi

Summary

Introduction

Many typhoid cases present as non-specific acute febrile illnesses that may be difficult to differentiate from other common tropical infectious diseases such as dengue and leptospirosis. There were an estimated 11.9 million (9.9 to 14.7) cases of typhoid in low and middle income countries in 2010, resulting in 129,000 (75,000 to 208,000) deaths [5]. Fiji is an upper middle income country with an estimated population of 892,000 in 2015 [6] across 100 inhabited Pacific Ocean islands, predominantly residing on Viti Levu and Vanua Levu [7]. Viti Levu comprises the Western and Central Divisions, the latter containing the capital Suva. Northern Division comprises of Vanua Levu and Taveuni island, whilst Eastern Division comprises of smaller island groups

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Discussion

Conclusion