The disease detectives: how epidemiologists investigate the source of infections

WHO Bangladesh/ Marshall

Cox’s Bazar, Bangladesh - It’s a hot day at Cox’s Bazar as two epidemiologists from WHO’s emergency field office arrive at a Rohingya camp to investigate a suspected cholera outbreak. A day ago, two children in a household of six, had fallen severely ill and been hospitalized.

Now the rapid response team of Dr Khadimul Anam Mazhar and Dr Katri Jalava have been tasked with finding out as much as they can about the cause of their illness.

As investigators, the job of epidemiologists is to identify the source of transmission of a suspected disease outbreak. Although the children had already tested positive for cholera through the Rapid Diagnostic Testing, the result is not definitive. A more precise test is done at the globally respected diarrhea research facility in Dhaka, the International Centre for Diarrheal Disease Research, Bangladesh.

The highly trained WHO epidemiologists analyze these laboratory tests and use their knowledge of how diseases spread, to piece together the complete picture. They determine the likely cause of illness and recommend a course of action.

The experts and International Organization for Migration (IOM) camp staff, together with government observers, systematically visit neighbors within the same block to ask if they had experienced similar symptoms. They enquire about episodes of diarrhea, vomiting or stomach ache, and check everyone’s immunization status. If vaccination records are lost or missing, which is not unusual in a relief camp, the epidemiologists try to get more information from parents or in their absence, from the local majhi, the official camp representative.

WHO Bangladesh

Their process is thorough, as they also consult nearby shopkeepers, teachers at the nearest playing areas and even some passersby, to see if anyone has reported diarrhea symptoms. Water, sanitation and hygiene experts from WHO and UNICEF inspect nearby water supplies to check out possible sources of contamination. The UNHCR/UN-Habitat WASH teams have taken samples from wells, handpumps and household drinking water containers, testing them for the gut bacteria E. coli.

WHO Bangladesh/ Marshall

Some households revealed very high levels of fecal contamination during the tests. A community education programme was recommended to teach residents how to avoid the spread of waterborne diseases.

WHO Bangladesh/ Marshall

Drs Mazhar and Jalava investigation results however are more encouraging. They are able to rule out a cholera outbreak and conclude that the diarrhea suffered by the children was the result of eating fermented fish. The meal had been shared by several neighbors who were only mildly affected. The two children were sent home the next day and their parents given advice on improving food and water hygiene.

‘Our team’s work is a great example of a quick response to a potentially serious outbreak,’ said the Head of WHO’s Cox’s Bazar Field Office, Dr Eigil Sorensen. ‘Rapid assessment, close teamwork and cooperation between the health sector and WASH partners familiar with the camp, are vital to stopping the spread of infection among people living in such overcrowded conditions.’