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Existing Ebola virus case definitions demonstrate low sensitivity
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Recently published data suggested that current Ebola virus disease case definitions are not sufficiently sensitive to identify all cases of the disease.
Patients who presented to Connaught Hospital in Freetown, Sierra Leone, during the West African Ebola outbreak were screened for suspected Ebola virus disease and admitted to the Ebola holding unit for isolation and diagnosis if necessary.
In a retrospective cohort study, researchers evaluated admission selection among these patients by identifying clinical characteristics predictive of a confirmed Ebola diagnosis. Patients were classified as confirmed Ebola virus disease cases or noncases based on the results of reverse-transcriptase PCR. The researchers recorded major risk factors for exposure such as “travel to an Ebola virus disease hot spot area, health care work, funeral attendance or contact with an ill family member or friend.”
From May to December 2014, 850 patients with suspected Ebola were admitted to the holding unit. PCR test results for 724 of these patients showed an Ebola diagnosis was confirmed in 64% of cases. Risk factors for exposure were identified in 22% of confirmed cases and 15% of noncases.
The most common presenting symptoms in suspected cases included fever or history of fever (83%), intense fatigue or weakness (68%), vomiting or nausea (50%) and diarrhea (41%). Intense fatigue, confusion, conjunctivitis, hiccups, diarrhea or vomiting was associated with an increased likelihood of confirmed Ebola. Three or more of these symptoms increased the likelihood of Ebola (OR = 3.2; 95% CI, 2.3-4.4).
The sensitivity of diagnosing Ebola virus disease based on these symptoms and risk factors in suspected cases, however, was 57.8%. Twenty-eight percent of confirmed noncases also presented with three or more of the presenting symptoms, corresponding to a specificity of 70.8%. In a subgroup analysis, 9% of confirmed Ebola cases did not report a history of fever or a risk factor of Ebola virus disease exposure.
“Inappropriate case definitions and delayed recognition of Ebola virus disease cases might have contributed to early failure of disease control in the current West African outbreak,” the researchers wrote.
They recommended that clinicians use a high degree of clinical suspicion in confirming Ebola virus disease cases.
“An accurate rapid diagnostic test is urgently needed,” the researchers said. “If an Ebola virus disease outbreak of such a size is to be avoided in the future, ensuring sufficient Ebola holding unit capacity with appropriate diagnostic support from the outbreak onset should be a priority.” – by Tina DiMarcantonio
Disclosure: The researchers report no relevant financial disclosures.
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