Author: Robert Colebunders
Position: MD, PhD
Institution: Institute of Tropical Medicine and University of Antwerp, Antwerp, Belgium
E-mail: bcoleb@itg.be
Additional Authors: De Roo Ann Institute of Tropical Medicine, Anwerp, Begium; Muyembe-Tamfum Jean Jacques, Institut National de Recherche Biomedical, Kinshasa, Republique Democratique du Congo; Guimard Yves, Medecine Interne-Maladies Infectieuses, Centre Hospitalier Jacques Coeur, Bourges, France
Submitted Date: December 27, 2005
Published Date: January 5, 2006
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

We read with interest the paper by Jonathan Cohen (1) about the lessons learned from the 2000 Ugandan Ebola outbreak (2). Recently we learned that the reservoir of the Ebola virus could be bats (3) and how the Ebola virus infects cells (4). A very important public health question, however, remains incompletely answered: how do filoviruses enter the human body? The Ugandan outbreak illustrates how infectious the Ebola virus can be through contact with blood and body fluids, but it remains unclear how exactly a person becomes infected.

During the 1995 Kikwit Ebola haemorrhagic fever (EHF) outbreak, we carried out a case-control study to determine the risk factors for acquiring EHF by health care workers (HCW). Cases were HCW of the two Kikwit hospitals and the Mosango hospital, considered to be 'clinical cases or confirmed EHF cases' according to the definitions used by the international team that was established to control the outbreak (5). Controls were HCW of the same hospitals who also had been in contact with an EHF patient, but who never developed clinical symptoms of EHF. Cases included persons who died of EHF and convalescent patients.

Convalescent patients and controls were interviewed using a standard questionnaire but with many open questions. The information concerning persons who died of EHF was obtained by interviewing several colleagues who had been working together with the person who died. Because of the open questions type of questionnaire and the difficulty in obtaining information about HCW who died, data about certain risk factors were incomplete.

Of the 120 participants in the study, 39 (32.5%) were cases and 81 (67.5%) controls. Among the 39 cases, 32 (82%) had died and 7 (18%) were convalescent. In a multi-variant analysis the following risk factors were identified: unprotected contact with the blood of an EHF patient, the manipulation of a corpse and the contact with several EHF patients. Hand-washing was protective. Hand-washing after patient contact was reported in 22(61.1%) of 36 cases, compared with 53(88.3%) of 60 controls for which reliable information was available (p=0.001).

Only one nurse became infected after a needle stick through her gloves when recapping a needle. Only two cases reported small wounds at the level of the hands as a possible entry point for the virus. One of the Italian nurses who became infected always worked with gloves, a mask and a blouse, but without goggles. She mentioned that she probably became infected by touching her eyes with a contaminated glove.

Factors explaining the high transmission rate of filoviruses to health care workers could be the high viral load, and the fact that filoviruses cause an acute and aggressive disease characterised by bleeding (often massive), vomiting and diarrhoea. It is our hypothesis that most filovirus infections are transmitted through contact of contaminated hands with the mouth mucosa or conjunctiva. Simple hand washing could reduce this transmission risk dramatically.

References
1. Cohen J (2004) Containing the threat - Don't forget Ebola. PLoS Med 1(3): e59.
2. Lamunu M, Lutwama JJ, Kamugisha J, Opio A, Nambooze J, et al. (2004) Containing a haemorrhagic fever epidemic: The Ebola experience in Uganda (October 2000 - January 2001). Int J Infect Dis 8: 27-37.
3. Leroy EM, Kumulungui B, Pourrut X, Rouquet P, Hassanin A, Yaba P et al. Fruit bats as reservoirs of Ebola virus. Nature. 2005 Dec 1;438(7068):575-6.
4. Kawaoka Y. How Ebola virus infects cells? New England Journal of Medicine 353: 25:2645-6.
5. Khan AS, Tshioko FK, Heymann DL, Le Guenno B, Nabeth P, Kerstiens B, et al. The reemergence of Ebola hemorrhagic fever, Democratic Republic of the Congo, 1995. Commission de Lutte contre les Epidemies a Kikwit. J Infect Dis. 1999 Feb;179 Suppl 1:S76-86.