5 Ebola patients in Kikwit outbreak had no physical contact to explain transmission, and scientists suggest other mechanisms

The following paper was written by CDC scientists in 1999.

J Infect Dis. 1999 Feb;179 Suppl 1:S92-7. 

Ebola Hemorrhagic Fever, Kikwit, Democratic Republic of the Congo, 1995: risk factors for patients without a reported exposure. 

Roels TH1, Bloom AS, Buffington J, Muhungu GL, Mac Kenzie WR, Khan AS, Ndambi R, Noah DL, Rolka HR, Peters CJ, Ksiazek TG.

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Abstract

In 1995, 316 people became ill with Ebola hemorrhagic fever (EHF) in Kikwit, Democratic Republic of the Congo. The exposure source was not reported for 55 patients (17%) at the start of this investigation, and it remained unknown for 12 patients after extensive epidemiologic evaluation. Both admission to a hospital and visiting a person with fever and bleeding were risk factors associated with infection. Nineteen patients appeared to have been exposed while visiting someone with suspected EHF, although they did not provide care. Fourteen of the 19 reported touching the patient with suspected EHF; 5 reported that they had no physical contact. Although close contact while caring for an infected person was probably the major route of transmission in this and previous EHF outbreaks, the virus may have been transmitted by touch, droplet, airborne particle, or fomite; thus, expansion of the use of barrier techniques to include casual contacts might prevent or mitigate future epidemics.

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Of the 23 patients in our study who were subsequently determined to have had previous exposure to a case of EHF, 19 had merely visited another patient with EHF and were not involved in patient care. None reportedly had any contact with patient blood, feces, vomitus, urine, or saliva, although 14 reported touching a patient with EHF. Recent immunohistochemical examination of skin biopsy specimens from patients with EHF has demonstrated viral antigens in skin and sweat glands [16], supporting the hypothesis that EHF may have been transmitted to these individuals in Kikwit (and others in previous outbreaks) by brief, unnoticed, superficial contact with EHF-in-fected persons.
The transmission mode in the 5 patients who became infected without any physical contact remains enigmatic. However, animal experiments have documented transmission of EBO virus via noncontact routes. For example, both guinea pigs and monkeys have been infected experimentally with EBO virus by direct installation of drops into the eye and throat [17]. Transmission of EBO virus from experimentally infected monkeys to control monkeys in separate cages has also been documented [18]. Furthermore, airborne spread was suggested during the EBO epizootic outbreak in Reston, Virginia [19, 20, 21]. In a review, Peters et al. [22] concluded that although the major mode of interhuman transmission of hemorrhagic fevers is direct contact, transmission via large droplets, aerosolized particles, or fomites cannot be excluded. This may explain the mode of transmission in the 5 patients without reported physical contact