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.

 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. 


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.

Here is the free full text, from which the next 2 paragraphs were extracted:

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

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