find the strength and weakness of this paper Case definition When the team reached the field, we made a very broad case definition as a method to include as many diseased cases as possible for blood sample collection for testing and confirmation. Our field case definition was any patient who developed a sudden high-grade fever ≥38 ◦C with or without bleeding, jaundice, vomiting or prostration after October 1. We used this case definition to guide our hospital visits, to facilitate active household case searching and to assist with clinical records revision.

criticize Case definition When the team reached the field, we made a very broad case definition as a method to include as many diseased cases as possible for blood sample collection for testing and confirmation. Our field case definition was any patient who developed a sudden high-grade fever ≥38 ◦C with or without bleeding, jaundice, vomiting or prostration after October 1. We used this case definition to guide our hospital visits, to facilitate active household case searching and to assist with clinical records revision.

criticize Active case finding The team conducted a systematic active casefinding survey based on the above field case definition. The team visited the two main hospitals of the affected area (Nertiti rural hospital and Nyala) and actively assessed the present medical records, admission sheets, laboratory registers and pharmacy logbooks. Additionally, ‘‘shoe-leather epidemiology’’ was used for active case finding at the village and household levels within the residential areas from which the index cases were reported. The investigation team visited the following villages during the field outbreak investigation missions: • Khour Ramla, • Fukodoko, • Rijl Aldalaba, • Toor, • Tibbi, • Jurfambari, • Norma. Based on the above-mentioned case definition, the investigation team generated the initial outbreak line list. Nine additional cases were added as a result of active case finding, bringing the total to 16 cases for the initial line list. Fresh blood samples were collected from the acutely febrile patients during the household visits (the samples were used for serology and blood films for malaria). Descriptive epidemiology The team analyzed the data descriptively, applying the classical epidemiological traits of person, place and time to gain insights on the reported cases. One of the most interesting findings was that the majority (81.2%) of the cases were young adult males, were related and were in close contact with animals (38% pastoral). Another interesting finding was that most of the cases were initially treated with antimalarial medications, including the recommended treatmentlines that are based on a positive immuno chromatographic (ICT) test for Falciparum Malaria. Family history ofthe disease was confirmed because two families had reported the deaths of immediate family members during the investigation period and the illness had manifested identically in both, with fever and bleeding (hematemesis). Bleeding presented in 80% of cases, while jaundice presented in 19% of cases. Further descriptions of the overall outbreak and the other reported cases will be published separately (Figs. 1 and 2). Hypothesis generation Before laboratory confirmation of the collected blood samples, the investigators generated three hypotheses based on the available descriptions for the reported cases and the surrounding environment, in addition to information from previous

4. What is a test case?

A case study is an example of:

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