Oct 16, 2014

Who Tests the Ebola Testers?

There is good reason to believe that one of the primary reasons for the initial spread of Ebola in this West African outbreak was improper laboratory testing procedures (see Chronology of the Ebola Outbreak in West Africa). Laboratory testing is crucial in an Ebola epidemic. Clinicians rely heavily on it in determining who is isolated and treated as a confirmed Ebola case and who gets sent back into the general population. The lab test is also the final arbiter of those who have officially survived Ebola, are no longer infectious and can be sent back to their communities. The lab test even determines the fate of the dead. An Ebola corpse is highly infectious and must be buried without delay and with elaborate safety precautions. A non-Ebola corpse can be buried with observance of normal funeral rites. In Sierra Leone during this epidemic, all deaths that occur outside hospitals are considered potential Ebola cases; families are required to obtain an Ebola status certificate after a swab/lab test before burial.

Ebola testing laboratories are under a considerable amount of pressure. There is great time sensitivity surrounding the outcome of their tests. If doctors do not receive test results speedily, patients have to be kept for long periods in holding centers, subject to cross infection with others in these centers. If the status of the dead is not declared speedily corpses begin to rot in homes, spreading infection and causing great unease in the community. As the epidemic has mushroomed so has the demand for tests, and the laboratories have at times been hard pressed to meet the demand. At first in Sierra Leone there was just the one Ebola laboratory, in Kenema, then a second run by the Canadians in Kailahun, then a third, South African, lab in Freetown, a fourth, Chinese, lab, also in Freetown and now a fifth, CDC, lab in Bo.

All tests are subject to error. The Ebola test, in particular, is said to be highly sophisticated and sensitive. From the regular Sierra Leone Ministry of Health updates we know that some patients have to be retested, when their clinical symptoms conflict with the lab test result. Errors in tests could be divided into two broad categories: false positives and false negatives. Both are problematic. The false positive test result incorrectly labels a patient who does not in fact have Ebola. This patient would then under normal circumstances be sent to an Ebola treatment center, where he/she would be at high probability of going on to actually become infected with Ebola. So the false positives end up killing patients who otherwise would probably have recovered from whatever ailment they had.

The false negative test result, on the other hand, incorrectly labels a patient who does in fact have Ebola. Under normal circumstances this patient is then sent back to a general ward or released to his/her family. In either case all those in close, unguarded contact with the patient will be liable to Ebola infection. In the case of highly infectious Ebola corpses, the false negative exposes mourners and those preparing the body for burial to the disease.

With so many labs in Sierra Leone from different countries and under such pressure, is there a need for independent testing of the testers? Is our Ministry of Health checking for consistency of test results within each lab and across all labs? Already one hears rumors within the public as to which labs are doing the ‘real’ tests and which are not. Experience from earlier in this outbreak teaches us that if even one lab is delivering a significant percentage of false results this could be disastrous for the course of this outbreak.