Research Article: Sensitivity, Specificity, and Public-Health Utility of Clinical Case Definitions Based on the Signs and Symptoms of Cholera in Africa

Date Published: April 26, 2018

Publisher: The American Society of Tropical Medicine and Hygiene

Author(s): Johara Nadri, Delphine Sauvageot, Berthe-Marie Njanpop-Lafourcade, Cynthia S. Baltazar, Abiba Banla Kere, Godfrey Bwire, Daouda Coulibaly, Adele Kacou N’Douba, Atek Kagirita, Sakoba Keita, Lamine Koivogui, Dadja E. Landoh, Jose P. Langa, Berthe N. Miwanda, Guy Mutombo Ndongala, Elibariki R. Mwakapeje, Jacob L. Mwambeta, Martin A. Mengel, Bradford D. Gessner.

http://doi.org/10.4269/ajtmh.16-0523

Abstract

During 2014, Africa reported more than half of the global suspected cholera cases. Based on the data collected from seven countries in the African Cholera Surveillance Network (Africhol), we assessed the sensitivity, specificity, and positive and negative predictive values of clinical cholera case definitions, including that recommended by the World Health Organization (WHO) using culture confirmation as the gold standard. The study was designed to assess results in real-world field situations in settings with recent cholera outbreaks or endemicity. From June 2011 to July 2015, a total of 5,084 persons with suspected cholera were tested for Vibrio cholerae in seven different countries of which 35.7% had culture confirmation. For all countries combined, the WHO case definition had a sensitivity = 92.7%, specificity = 8.1%, positive predictive value = 36.1%, and negative predictive value = 66.6%. Adding dehydration, vomiting, or rice water stools to the case definition could increase the specificity without a substantial decrease in sensitivity. Future studies could further refine our findings primarily by using more sensitive methods for cholera confirmation.

Partial Text

Cholera remains a major public-health issue in developing countries. In Africa, 3,221,050 suspected cases were notified to the World Health Organization (WHO) from 1970 to 2011, which represented 46% of all suspected cases reported worldwide.1 During 2014, Africa reported 105,287 cases, which represented an increase of 87% compared with the previous year2; The Democratic Republic of Congo (DRC), Ghana, and Nigeria recorded 83% of all African cases.3 Case fatality ratios were higher than 5% only in African countries and included Cameroon, Côte d’Ivoire, Guinea Bissau, and Kenya and Africa recorded 84% of deaths globally. The high values for disease burden in sub-Saharan Africa, however, may underestimate substantially the total disease burden. For example, some countries likely under-notified cases possibly because of fear of stigmatization: Gabon and Central African Republic did not report any cases from 2008 and 2004, respectively, even though their neighboring countries were regularly affected with cholera epidemics.4,5

A total of 9,391 suspected cholera cases were enrolled in the study from June 2011 to July 2015, with almost half (43.4%) from the DRC, followed by Guinea (20%) and Mozambique (14%) (Table 3). More than 54% of the suspected cases (5,084) had a culture test done, of which 1,816 (35.7%) were confirmed for V. cholerae. Goma and its suburbs in DRC represented 60% of culture-confirmed cases. The proportion of men and women was approximately the same within the categories of suspected and culture-tested cases.

In using data from 27 sites located in seven African countries, we found that the WHO case definition for cholera had high sensitivity and low specificity overall and among all subgroups. This is likely because almost all true cholera cases typically had acute watery diarrhea but most patients with acute watery diarrhea did not have cholera, even in outbreak sites. Use of a highly sensitive definition facilitates the timely detection of outbreaks and may be appropriate given the potential for cholera to rapidly cause large outbreaks or national epidemics.18–21 However, the lack of specificity may lead to excessive interventions or inappropriate distribution of resources. Adding the presence of other symptoms to the WHO case definition used during outbreaks—such as dehydration, vomiting, or rice water stools—substantially increased specificity with only a minimal decrease in sensitivity. Other studies of cholera have shown that the same clinical signs were associated with culture positivity among suspected cholera cases.10 For example, in Bangladesh, diarrhea, vomiting, and dehydration were more frequent in culture-positive cases.22 As in Haiti,23 we found that persons with longer hospitalization periods were more likely to have dehydration and signs of dehydration compared with persons hospitalized less than a day.

 

Source:

http://doi.org/10.4269/ajtmh.16-0523

 

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