EBOLA TRANSMISSION

Epidemiological studies have suggested that the Ebola virus spreads primarily through direct contact with a symptomatic person or their body fluids, especially in the latter stages of clinical disease.Reference Dowell, Mukunu and Ksiazek ^{5 ,} Reference Francesconi, Yoti and Declich ⁶ The elevated risk of transmission in the latter stages of EVD is likely due to a combination of increased viral titers in body fluids and increased body fluid discharges (ie, vomitus, stool, and blood). Post-mortem contact is also associated with a high risk of Ebola virus transmission.Reference Dowell, Mukunu and Ksiazek ⁵ Concern has been raised regarding the possibility of aerosol transmission “either via large droplets or small particles in the vicinity of source patients.”Reference Osterholm, Moore and Kelley ⁷ Although animal studies suggest that droplet/airborne transmission may occur when the virus is experimentally aerosolized, epidemiologic studies of household contacts suggest that this rarely, if ever, occurs.Reference Dowell, Mukunu and Ksiazek ^{5 ,} Reference Francesconi, Yoti and Declich ^{6 ,} Reference Johnson, Jaax, White and Jahrling ⁸ However, there is concern that droplet or airborne transmission could occur in healthcare settings during aerosol-generating procedures such as intubation and induced sputum collection.

The fact that Ebola has been demonstrated to survive and remain infectious in liquid media at room temperature for at least 46 days raises concern about fomite transmission.Reference Piercy, Smither, Steward, Eastaugh and Lever ⁹ Ebola inoculated onto glass carriers and maintained in the dark survived for hours to days (ie, 1-log₁₀ decrease in 35.3 hours and 4-log₁₀ decrease in 5.9 days).Reference Sanripanti, Rom and Holland ¹⁰ Some epidemiologic studies have suggested the possibility of transmission from contaminated environmental sources.Reference Francesconi, Yoti and Declich ⁶ Further, in the current outbreak, multiple environmental samples from an Ebola treatment unit were positive via polymerase chain reaction (PCR) testing.Reference Osterholm, Moore and Kelley ⁷ However, in a different study in which sampling was done following routine cleaning, all 31 environmental samples were negative by reverse-transcriptase PCR (RT-PCR), suggesting that routine environmental cleaning and disinfection can decrease the potential for fomite transmission.Reference Bausch, Towner and Dowell ¹¹

PREVENTING EBOLA ACQUISITION BY HCP

As noted above, a substantial number of HCP in West Africa have acquired EVD. Nosocomial transmission of Ebola and infection of HCP has been repeatedly documented in past outbreaks.Reference Kerstiens and Matthys ^{12 –} Reference Khan, Tshioko and Heymann ¹⁴ The cluster of Ebola cases in Dallas is illustrative of the 2 major risks for Ebola acquisition faced by US HCP.Reference Chevalier, Chung and Smith ^{15 ,} Reference Chung, Smith and Weil ¹⁶ First, early recognition, triage, and isolation of all potential EVD cases are essential so adequate infection control measures can be applied and potential transmission of Ebola virus to HCP can be minimized. Second, the acquisition of EVD by 2 HCP who had substantial interaction with an Ebola patient while wearing protective equipment raised concern regarding the adequacy of protection afforded by personal protective equipment (PPE) or the training provided in its use.

The basis for preventing the spread of infectious agents in healthcare facilities is the implementation of transmission-based precautions, which includes different room placement (ie, private room or airborne isolation room) and HCP use of PPE (gloves, gowns, mask, N95 respirator, and/or face shield) based on the mechanism of transmission of the infectious agent (ie, contact, droplet, airborne).Reference Siegel, Rhinehart, Jackson and Chiarello ¹⁷ Given the acquisition of Ebola by HCP in Dallas and the large number of HCP in West Africa, 2 key questions have arisen. First, what is the evidence that PPE protects HCP from acquiring a contact transmitted disease? Second, what steps can we take to minimize the risk to HCP of acquiring EVD while caring for an infected patient?

The gloves and gowns of HCP frequently become contaminated with pathogens while providing care to patients on contact precautions. Recently, Williams et alReference Williams, McGraw and Schneck ¹⁸ reported that HCP frequently contaminated their clothing despite wearing gloves and gowns for patient care. Casanova et alReference Casanova, Alfano-Sobsey, Rutala, Weber and Sobsey ^{19 ,} Reference Casanova, Rutala, Weber and Sobsey ²⁰ assessed the ability of standard PPE (ie, gloves, gowns, respirator, and goggles) to protect against contamination of skin and clothes by dotting the outside of the PPE with bacteriophage MS2, a nonenveloped, nonpathogenic RNA virus. PPE was removed using the CDC-recommended doffing procedure. Initial experiments revealed that underlying clothing (scrub shirt, pants) and skin (dominant and nondominant hand) were contaminated >70% of the time.Reference Casanova, Alfano-Sobsey, Rutala, Weber and Sobsey ¹⁹ Further, the mean viral titer recovered was 1.8–2.4-log₁₀ (inoculating dose = 10₄ on several PPE sites). Despite double gloving, skin contamination (6%–23%) and clothing contamination (56%–94%) remained common.Reference Casanova, Rutala, Weber and Sobsey ²⁰ The failure of standard PPE to protect HCP against skin and clothing contamination and the lack of validation of the level of protection afforded by PPE recommended for Ebola care have raised concerns.Reference Sprecher, Caluwaerts and Draper ²¹

At the present time, it is recommended that HCP providing care to a patient with EVD use enhanced PPE.Reference Fischer, Weber and Wohl ²² Although there is no consensus on each of the specific components of PPE among the major organizations providing care to EVD patients, all agree that it should uniformly protect the major portals of entry including mucous membranes and nonintact skin. CDC guidelines, which are directed toward the use of PPE in US hospitals, recommend double gloves, a single-use fluid-resistant gown or coverall, an impervious apron, and either a powered air-purifying respirator (PAPR) or an N95 respirator. If the latter is used, then it must be accompanied by a single-use surgical hood extending to the shoulders and a full face shield. Critical to maximizing PPE protection are detailed donning and doffing procedures, comprehensive training on proper donning and doffing, and use of a monitor to ensure proper donning and doffing.Reference Fischer, Weber and Wohl ²²

As demonstrated by Casanova et al, the major risk to the HCP is that during the doffing procedure contamination of underlying clothes or skin may occur. This raises the question of whether additional methods may be used to further protect the HCP such as decontamination of the PPE prior to removal by either ultraviolet light (UV) or use of a germicide (eg, hypochlorite). In this issue, Tomas et alReference Tomas, Cadnum, Jencson and Donskey ²³ report that a portable booth using UV-C radiation can be used to disinfect full-body PPE. They demonstrated that the delivered UV-C radiation resulted in ≥3-log₁₀ reduction in MS2 virus and methicillin-resistant Staphylococcus aureus (MRSA) within 3 minutes. Additionally, UV-C radiation has been demonstrated to inactivate the Ebola virus.Reference Sagripanti and Lytle ²⁴ Although the UV-C booth may reduce the risk of skin/clothing contamination during the doffing procedure, it may be impractical for use in lesser-developed countries. Another strategy to mitigate the risk of skin/clothing contamination during doffing would be to decontaminate the outside of the PPE using a germicide applied by spray or wipe such as hypochlorite (diluted bleach).Reference Rutala and Weber ²⁵ However, although this procedure has often been used in the field, there is considerable debate about the use of sprays because of concern for aerosolizing laden body fluids that may contaminate the PPE.

To protect our HCP against acquisition of highly virulent pathogens such Ebola, we must assess all the potential risks for transmission (eg, inadequate detection of possible cases, inappropriate use of PPE) and implement strategies to minimize this risk (Table 1). The public health community needs to reduce the risks to our HCP by validating the currently recommended PPE, improving PPE as necessary, improve training of our HCP, and expand the number of facilities with healthcare units specifically designed to care for highly communicable diseases. We need to continue to develop innovative approaches such as that assessed by Dr. Tomas.

TABLE 1

Protecting Healthcare Personnel from Acquisition of Ebola: Defining the Problems and Possible Solutions

NOTE. TSA, Transportation Security Administration; ED, emergency department; EVD, Ebola vial disease; HCP, healthcare personnel; PPE, personal protective equipment.

Finally, HCP at all US hospitals need to remember that more than 1 million travelers arrive in the United States each week. ²⁶ As demonstrated by the recent case of Lassa fever in New Jersey, ²⁷ the outbreak of MERS-CoV in Korea, ²⁸ and the Ebola cases resulting from travelers from West Africa,Reference Bogoch, Creatore and Cetron ²⁹ we are all only a plane ride away from potentially highly communicable and virulent infectious diseases.