Consider this scenario: A healthcare worker dons a surgical mask to enter the room of a patient on droplet precautions for respiratory infection. The diagnosis is updated when it is discovered that the patient actually has TB, which calls for airborne precautions that require an N95 respirator or something equivalent. Should the healthcare worker who wore the surgical mask be considered exposed to TB?

“To the best of my knowledge, there has never been a healthcare worker who acquired TB because they were just wearing a surgical mask,” said David Weber, MD, MPH, an epidemiologist and professor at the University of North Carolina School of Medicine in Chapel Hill. “That said, there is no question that when you do air flow studies that an N95 has better filtering capacity both through the mask and, more importantly, around the mask because it is a better, tighter fit. But we wouldn’t treat somebody wearing a surgical mask — if they wore it properly — if [the TB patient] was mistakenly put on droplet precautions. We wouldn’t consider that an exposure.”

The lead author of a recently published paper1 on healthcare exposures to infectious agents and post-exposure treatment, Weber fielded questions on the topic in a wide-ranging interactive session recently at the IDWeek 2016 conference.

“What is the [TB] risk if you don’t wear a mask at all?” he said. “We’ve looked at our data, and if you look at the CDC guidelines they don’t consider it an exposure [until after a certain] number of hours. So walking into a room for 20 minutes would not be considered an exposure. If you are on a plane with [someone who has] TB, they only track you down if you are on the plane for more than four hours. So recognize that time is also relevant. When we have looked over 30 years, the risk [of infection] after being exposed to TB — we’ve never tried to break it down by time; we don’t have enough data — is about 0.5%. So there is about a 1 in 200 risk of converting your TST test or your IGRA if you take care of a TB patient without wearing a mask.”

Of course, there are outliers on either end of the spectrum, given the variables in a patient’s infectivity, the worker’s immune status, and nature of the interactions.

“We’ve had cases in the olden days where they didn’t wear masks routinely during bronchoscopy, and everybody in the bronchoscopy suite converted,” he said. “We have had patients in the hospital for weeks before they made the diagnosis of TB and no one converted.”

If employee health determines an exposure has occurred, Weber recommended moving out from the index case in concentric circles depending on healthcare worker contact.

“If we have lots of people, we look the most exposed,” he explained. “If we see any conversions, we will go to the people less exposed and work our way out. [This is preferable] to just testing everybody, like someone in dietary who just came in to drop a tray off.”

The importance of counseling exposed workers is critical, particularly in situations where healthcare workers are concerned about becoming infected, said Tom Talbot, MD, co-speaker at the session and epidemiologist at Vanderbilt University School of Medicine in Nashville. He described a disturbing case of the death of patient with meningitis, which was followed by the need to determine which workers were exposed and who needed post-exposure prophylaxis.

“We had a very devastating case of a 19-year-old college freshman that came in with meningococcal disease, was the in the ED and being coded for about 90 minutes, and passed away,” he said. “It was a very traumatic experience for the healthcare workers, and then later on they became worried about their risk. I remember sitting in the ED for about two hours and folks were coming in and saying, ‘I did this, I walked into the room, I handed some supplies,’ and asking, ‘Am I at risk?’ That is probably the most striking example. This is really important because people see this horrible illness and then they get scared. It is really important to remember that piece of it. Often the risk is still fairly low, but just reassuring them and particularly [underscoring] prophylaxis if they do need it.”

For exposures in general, it is often a matter of practicality to delineate those exposed from those nonexposed as the point when the decision was made to place the patient in isolation, Talbot noted.

“But in the real world, there are people who come into the room without wearing all the PPE, and other factors,” he said. By the same token, it is sometimes more workable to consider those exposed as those who entered the room when the patient was undiagnosed rather than trying to determine if they got within, for example, three to six feet from the patient.

“We used to have a policy that if you were immune [to the patient’s infection], you didn’t have to wear PPE,” Talbot said. “We stopped that and I think more places are stopping that for a couple of reasons. One, vaccines are not 100% effective, so workers are still at risk, but I think perhaps more importantly is if other healthcare workers see me [not wearing PPE on room entry]. They don’t know my immune status and may think it is not necessary to wear PPE to go into the room. You can’t explain that in real time, and people see your behaviors so [our policy now] applies to everybody. You walk in the door, you wear the stuff. Yes, you spend some money on PPE, but you reduce the risk of someone getting exposed.”

In the wake of the widespread PPE problems reported during the Ebola outbreak, the CDC is piloting some tools that would require observation of workers donning and doffing protective equipment, Talbot said. The concept is theoretically sound, but may be labor-intensive in facilities with a large number of employees, he noted.

“The health department in Tennessee is piloting this CDC tool,” he said. “It is much more prescriptive on how you train your healthcare personnel not only in hand hygiene, but the use of PPE to the point of hands-on annual competency of all personnel — not just watch a PowerPoint every year, but actually watching them put on and take off the PPE. The other piece of it would be — like we monitor handwashing — really prescriptively tracking how well we use our PPE in precautions and feeding that back to folks. That is something that has emerged from Ebola.”

In terms of post-exposure prophylaxis (PEP) for HIV, Weber reminded that occupational health requirements stipulate the use of the “most recent” public health recommendations.

“They take the [PEP] recommendations and make it a regulation, so as the guidelines get updated by the public health services for post-exposure prophylaxis for HIV — the timing, tests, drugs — you are bound to follow that guideline by law,” Weber said.

Another good measure to protect workers is to automatically implement isolation when a test is ordered; for example, measles.

“We don’t see much measles, mumps, or rubella, fortunately, but we do need to be concerned about those,” Weber said. “One of the problems with mumps is that it is not a rash disease and people don’t think of it when somebody comes in with a little swelling or just feeling poorly. And the problem with both measles and rubella is that, probably, most of the house officers and most of our junior faculty have never seen a case. We actually had an exposure with this because the Hare Krishna community was not receiving MMR vaccines. They have no philosophical oppositions to vaccines, but they are strict vegetarians and the vaccine is made in eggs.”


  1. Weber DJ, Rutala WA, et al. Occupational health update: Focus on preventing the acquisition of infections with pre-exposure prophylaxis and post-exposure prophylaxis. Infect Dis Clin N Am 2016;30:729-757.