Seroincidence of Enteric Fever, Juba, South Sudan

Abstract

We applied a new serosurveillance tool to estimate typhoidal Salmonella burden using samples collected during 2020 from a population in Juba, South Sudan. By using dried blood spot testing, we found an enteric fever seroincidence rate of 30/100 person-years and cumulative incidence of 74% over a 4-year period.

Keywords: Juba; Paratyphi; Salmonella enterica; South Sudan; Typhi; bacteria; enteric fever; enteric infections; salmonella; typhoidal salmonella.

Figure 1

Age-dependent hemolysin E (HlyE) IgA (top) and IgG (bottom) responses for participants in study of seroincidence of enteric fever, Juba, South Sudan, 2020, compared with those for blood culture-confirmed cases and controls. A) Cross-sectional antibody responses to HlyE IgA (top) and IgG (bottom) by age measured from a serosurvey of 1,290 persons in Juba, South Sudan, from samples during collected during August 7–September 2, 2020. Each point indicates an individual sample. Horizontal lines within boxes indicate medians; box tops and bottoms indicate IQRs; error bars indicate 95% CIs. B) Density of antibody responses HlyE IgA (top) and IgG (bottom) among 1,410 blood-culture confirmed enteric fever cases in Bangladesh, Nepal, Pakistan, and Ghana 8–12 months after symptom onset as reported in (12) and a control population from 3 United States groups: 48 children 1–5 years of age who had first degree relatives with celiac disease, enrolled nationally; 31 healthy controls, children and young adults 2–18 years of age, enrolled at Massachusetts General Hospital (Appendix reference 17); and a population-based sample of 205 children and adults 3–50 years of age participating in a SARS-CoV serosurvey in California, USA. The dashed blue line across all panels represents the mean +3 SD of HlyE IgA and IgG values observed in the pediatric control population. HlyE, hemolysin E.

Figure 2

Estimated seroincidence of typhoidal Salmonella by age, Juba, South Sudan, 2020. A) Seroincidence per age group. Error bars indicate 95% CIs. B, C) Individually predicted incidence estimates (points) and smoothed cumulative incidence (lines) over 2-year (B) and 4-year (C) periods, by age. Gray shading indicates 95% CIs.