MMWR Details Discordant Ebola Case Definitions Among DRC and Bordering Countries

January 20, 2020

Investigators of a new analysis detail how Ebola case definitions became increasingly complex and discordant during the 6-month period in the countries surrounding the DRC.

In the initial stages of the Ebola outbreak response, countries neighboring the Democratic Republic of the Congo (DRC) adopted different Ebola case definitions according to historical context and perceived risk. Changes in case definition can move endemic countries toward or away from interregional coordination during an outbreak, making these definitions an area of interest for clinicians.

The authors of a new article published in the US Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report have examined case definitions used by neighboring countries during the initial 6 months of the Ebola outbreak in the DRC. The report details how Ebola case definitions became increasingly complex and discordant during the 6-month period.

When the DRC announced the nation’s tenth Ebola outbreak on August 1, 2018, the World Health Organization (WHO) designated Uganda, South Sudan, and Rwanda as high priority countries for Ebola preparedness due to the risk that the blood-borne disease could spread across borders.

The CDC coordinated with health officials in the DRC, South Sudan, Rwanda, and Uganda to assess the concordance of case definitions among the countries at 3 particular time points.

The 3 comparison dates were August 1, 2018 (the start of the outbreak), November 15, 2018 (the period before the peak in incidence), and February 1, 2019 (6 months into the outbreak).

Country-level revisions of case definition ranged from 2 to 4 during the period evaluated, reflecting that by February 2019 all countries had revised their Ebola definitions following the December 2018 peak in incidence within the DRC.

“Case definition complexity increased over time; all countries included more criteria per category than the WHO standard definition did, except for the ‘case contact’ and ‘confirmed’ categories. Low case definition concordance and lack of awareness of regional differences by national-level health officials could reduce effectiveness of cross-border communication and collaboration,” the authors of the article wrote.

South Sudan removed its ‘probable’ case definition category by November 2018, and Uganda did not include the category during the 6-month period. Rwanda did not include a community alert category until January 2019.

Uganda was the only country examined that included a ‘case contact’ category consistently during the 6 months.

Nonbleeding symptoms were included in most countries as criteria for suspected and community alert categories, but in Uganda, symptom criteria were limited to signs of unusual bleeding.

Some countries had no case definition threshold for fever, and some had 2 thresholds in operation simultaneously.

Concordance of criteria for case contact remained low throughout the period examined, increasing from 17% to only 20% during the 6-month span. There was 0 concordance of community alert definitions initially, which increased to 25% in November 2018 but declined back to 0 by the end of the period.

The article noted that a degree of different sensitivity thresholds may be reasonable due to resource availability, perceived risk, and prioritization. But high complexity and discordance of case definitions was consistent between countries examined across the initial 6 months of the DRC outbreak.

“Complexity of and discordance in case definitions affect information sharing about alerts and cases across national borders. The potential risk associated with this discordance to cross-border communication and collaboration during an outbreak with a threat of cross-border spread might warrant a move toward regional harmonization or tailored binational and multinational communication strategies,” the authors wrote.