Impact of Epidemic Cholera in a Previously Uninfected Island Population: Evaluation of a New Seroepidemiologic Method

Abstract

During an investigation of a 1982 cholera outbreak in Truk, an area without endemic cholera, 254 post-outbreak serum specimens were collected from ill and well inhabitants of a single island. These were compared with 57 specimens collected in Truk in 1964, when heat-labile toxin-producing enterotoxigenic Escherichia coli was presumably endemic but cholera did not exist. The serum was tested for vibriocidal antibody and antitoxic antibodies to cholera toxin and heat-labile toxin and the ratio of the anti-cholera antitoxin to the anti-heat-labile antitoxin was calculated. The prevalences of elevated anti-cholera antitoxin and anti-heat-labile antitoxin levels were similar in both years: an elevated anti-cholera antitoxin was found in 30% of the 1964 and 80% of the 1982 specimens, while an elevated anti-heat-labile antitoxin was found in 40% (1964) and 84% (1982). In contrast, vibriocidal antibody titers were elevated in none of the 1964 but in 64% of the 1982 specimens, and the anti-cholera/anti-heat-labile antitoxin ratio was elevated in 4% (1964) and 42% (1982). The anti-cholera/anti-heat-labile antitoxin ratio appears to differentiate the antitoxic responses to Vibrio cholerae O1 and heat-labile toxin-producing enterotoxigenic E. coli, even in areas where both are prevalent, and should serve as a useful seroepidemiologic tool.

Inferring the proportion of undetected cholera infections from serological and clinical surveillance in an immunologically naive population

“…Our estimates of the ratio of infections to reported clinical cholera cases are at the lower end of those previously reported, which likely reflects that this population had no previous exposure to the bacteria, but could also reflect differences in host factors (e.g., undernutrition) and exposure routes [11][12][13]20,21,[24][25][26][27]. Our estimated number of infections among young children nearly matches the numbers of reported suspected cholera cases, this either implies that there were almost no infections in this age group that did not results in medically-attended disease, or more realistically that unreported infections got compensated by the poor specificity of the suspected cholera case definition, especially in young children, where other etiologies frequently lead to similar symptoms.…”

“…Furthermore, most evidence comes from hyperendemic settings like Bangladesh, where exposure to cholera is extremely common. Despite the scientific consensus that the number of asymptomatic or mild infections is many times higher than the number of clinically relevant infections, estimates have varied widely (factor 2 to 100), likely as a result of variable case definitions, individual infection histories, different V cholerae strains and host factors (Supplementary Material) [11,13,[20][21][22][23][24][25][26][27]. Being able to translate between the number of cases observed at health facilities and the true number of infections in the community, or vice-versa, could help improve the public health utility of serosurveillance data and strengthen our understanding of cholera epidemiology and immunity.…”