Even workers with a history of measles vaccination or immunity should wear an N95 or equivalent respiratory protection when examining or caring for patients with suspected or confirmed measles, says Shruti K. Gohil, MD, lead author of a recent study on the issue and associate medical director of Epidemiology & Infection Prevention at the University of California, Irvine School of Medicine.
“You can acquire it even though you have been vaccinated and the impact of not wearing an N95 for infection prevention in terms of exposures is huge,” she says. “You can expose a lot of patients and cause a lot of worry about transmission.”
There is about a 3% risk of breakthrough infections even after measles immunization, so the CDC recommends wearing a respirator even if vaccinated when caring for patients with suspect or confirmed measles.
“One of the things we have difficulty with sometimes is that our healthcare workers will ask us, ‘How come I have to wear an N95 if I am already vaccinated against measles?,’” she says.
With measles declared eradicated in the U.S. in 2000, it fell off the clinical radar, leading to misdiagnoses and unrecognized cases as it began dramatically returning a decade later. The infected workers in this outbreak were exposed primarily through face-to-face contact with undiagnosed cases of measles, though given the patient symptoms N95 respiratory protection was probably warranted. Yet N95 respirator use by healthcare workers with documented immunity to measles is not uniformly required or practiced in hospitals, the authors observe.
“We know it’s not standardized practice to use N95s if you have been vaccinated against measles,” Gohil says. “They should wear N95s as soon as there is concern about potential measles in a patient. Recognizing those infected early [and following precautions] allows you to use resources appropriately. Your time and energy can go toward taking care of the patient as opposed to chasing down all the healthcare workers who may have exposed other patients.”
MORE THAN 1,000 EXPOSED
A community outbreak of measles in Orange County, CA, in 2014 led to secondary transmission to five healthcare workers. Of these, four had direct contact with measles patients and none wore N95 respirators. Four of the healthcare workers had prior evidence of immunity and continued working after developing symptoms, ultimately resulting in 1,014 exposures to patients and colleagues.
“They had proof of immunity but still got sick,” Gohil says. “They were very mild symptoms — that was pretty striking. They hardly knew that they were sick. You usually have symptoms of fever, cough, and cold-like symptoms. These healthcare workers had very little or none of that. The reason they continued to work is that they really didn’t feel that they were sick. It wasn’t until the [measles] rash showed up that clinicians were aware that something else was going on and that’s when they reported for care.”
Despite the relatively mild nature of the occupational infections, it certainly could not be assumed that transmission would not continue. Due diligence required the herculean follow-up of all exposures, none of whom contracted measles.
“In the literature, we know that if you are vaccinated you are less likely to acquire measles and it would make common sense that the presence of antibodies would limit the course of the illness and the likelihood that you would transmit to others,” she says. “We have hints and suggestions that this is true, but the fact that we had four symptomatic healthcare workers who saw all these other patients while they were actively infected, it resulted in a whole bunch of exposures. None of the exposures went on to acquire disease and that is important to note.”
Thus in an experiment of sorts that would never be approved as a clinical trial, the outbreak showed the vaccine is imperfect but it did apparently block subsequent transmission. “So as far as we know this is one of the few opportunities to [assess] the vaccine efficacy in limiting illness and preventing transmission,” she says.
Healthcare workers who have rarely seen a measles case may assume they are immune if they have been vaccinated or had natural infection as a child. Thus they may feel safe treating confirmed or suspect measles patients without respiratory protection and may even decide to disregard a hospital policy.
“I think most of hospitals do have these [N95] policies in place, but in practice they may see some resistance to this type of policy,” Gohil says. “I can say at my hospital, UC Irvine, we did have something in place for use of N95s.”
In addition, although most healthcare workers are required to have evidence of measles immunity as a condition of employment, enforcement of such policies is variable, the authors noted. Infection control and occupational health strategies often treat historical documentation of measles immunity as absolute, despite the low but present risk for measles infection in persons with evidence of immunity, they concluded.
The community outbreak in Orange County included 17 confirmed cases diagnosed from mid-January 2014 to April 21. The first identified measles case was a 19-year-old female with known exposure to measles during travel to the Philippines who developed disease despite three documented MMR vaccine doses. One cluster in the outbreak included a “vaccine-refusing family” which led to subsequent spread in a daycare center. As cases presented for care, a history of immunity provided “false reassurance” to healthcare workers with unprotected face-to-face exposures, leading them to continue working even when mild symptoms appeared.
“Our findings emphasize the importance of adherence to the recent CDC recommendation for use of N95 or equivalent respirator for suspect measles cases regardless of immunity status,” Gohil and colleagues concluded. After the outbreak, the facility began immediate triage of patients presenting with any rash, using signage to guide patients to enter the facility away from the emergency room waiting area and directly into airborne isolation until further evaluation.
- Gohil SK, Okubo S, Dickey L, et al. Healthcare Workers and Post-Elimination Era Measles: Lessons on Acquisition and Exposure Prevention. Clin Infect Dis 2016;62:166-172.