CDC calls for mumps shots, 100 HCWs infected in Iowa

Birth before 1957 not proof of immunity

With reports of more than 100 health care workers infected with mumps during a Midwest outbreak that now exceeds 4,000 cases, the Centers for Disease Control and Prevention is recommending that all health care workers should have immunity to mumps and even those born before 1957 should receive one dose of vaccine.

"There are 4,190 cases now throughout the country and about half of those are in Iowa," said Jane Seward, MBBS, MPH, a CDC epidemiologist in the division of viral disease "I think we are confident now that Iowa is over the peak of their outbreak. They are on the decline, but I don't think we can say that yet for the other states."

Indeed, the outbreak has spread into bordering Midwest states and threatens to surge again when college students return to campuses this fall. One-quarter of the cases in Iowa have been in college students, the group that has been fueling the outbreak and carries the highest risk of expanding it nationally. In light of the situation, the CDC held a special May 17 conference call with its Advisory Committee on Immunization Practices (ACIP) to update criteria for mumps immunity and mumps vaccination recommendations.

"The ACIP voted to change evidence of immunity to two doses for school-age children and high-risk adults," Seward said. "High-risk adults were defined the same way as they are for measles — students in post-high school educational facilities, international travelers, and workers in health care facilities. For health care workers, there was a change to recommend two [vaccine] doses routinely. For health care workers there [had been] just a one-dose recommendation and that is now two — the same as measles."

More than 100 health care workers in Iowa — the epicenter of the outbreak — have been infected with mumps since the traditional childhood disease resurged late last year, Seward reported at the June 1 meeting of the CDC's Healthcare Infection Control Practices Advisory Committee (HICPAC). However, the cases remain under investigation and no details were immediately available on such key questions as mode of transmission, infection control precautions in place, and vaccination history of the health care workers. The CDC emphasizes that infection- control failures resulting in nosocomial transmission have occurred during mumps outbreaks involving hospitals and long-term care facilities that housed adolescent and young adult patients. Exposures to mumps in health care settings also can result in added economic costs associated with furlough or reassignment of staff members from patient care duties or closure of wards.

Back to the '80s

The situation appears to be similar to the widespread mumps outbreaks that occurred in 1986 and 1987. In a study conducted in Tennessee during that outbreak, infection control problems caused by mumps were reported from 17 (12%) of 146 surveyed hospitals.1 The 17 hospitals in which these incidents occurred were located in counties that accounted for 67% of the reported mumps cases statewide during this period. Although most cases of mumps in health care workers were community-acquired, six health care workers in three different hospitals developed mumps following nosocomial exposure. In two institutions, nine patients contracted mumps while hospitalized. A similar study is under way in Iowa to determine whether the worker infections were acquired in the hospital or the community, and to investigate "anecdotal reports" of nosocomial transmission among patients and health care workers, Seward told HICPAC.

In guidelines released after the ACIP conference call, the CDC now recommends that: "All persons who work in health care facilities should be immune to mumps. Adequate mumps vaccination for health care workers born during or after 1957 consists of two doses of a live mumps virus vaccine. Health care workers with no history of mumps vaccination and no other evidence of immunity should receive two doses (at a minimum interval of 28 days between doses). Health care workers who have received only one dose previously should receive a second dose. Because birth before 1957 is only presumptive evidence of immunity, health care facilities should consider recommending one dose of a live mumps virus vaccine for unvaccinated workers born before 1957 who do not have a history of physician-diagnosed mumps or laboratory evidence of mumps immunity."2

Health care workers include people who provide health care to patients or work in institutions that provide patient care (e.g., physicians, nurses, emergency medical personnel, dental professionals and students, medical and nursing students, laboratory technicians, hospital volunteers, or administrative and support staff in health care institutions), the CDC explained.

The new recommendations for health care workers are intended to offer increased protection during a recognized outbreak of mumps, the CDC advised. However, reviewing health care worker immune status for mumps and providing vaccine during an outbreak might be impractical or inefficient. Therefore, facilities might consider reviewing the immune status of health care workers routinely and providing appropriate vaccinations, including a second dose of mumps vaccine, in conjunction with routine annual disease-prevention measures such as influenza vaccination or tuberculin testing, the CDC added.

Avoid 'unnecessary crisis'

"When we first drafted the health care worker guidance, it was suggested that birth before 1957 was adequate evidence for immunity for health care workers, but during an outbreak situation, you might want to give them one dose anyway," Michael Bell, MD, an epidemiologist in the CDC division of health care quality improvement, told Hospital Infection Control. "The reality is that an outbreak situation is the worst possible time to try and do that. It would be creating an unnecessary crisis. Instead, this is something that can be done routinely over the course of time, whether it is the second dose for routine health care worker vaccination or that one additional dose for someone born before 1957. This is something that can be worked into routine occupational health as part of your annual PPD [TB skin test]."

Discussions at the HICPAC meeting indicated that health care facilities also have the option of screening for antibodies to mumps rather than potentially vaccinating those already immune. While some may find it less expensive to check titers than simply vaccinate, use of the vaccine for post-exposure prophylaxis is not a good option. "Because of the very long incubation period for mumps — 16 to 18 days on average — it doesn't work," Seward said. "By the time somebody displays symptoms, those around them could have been exposed a good seven days ago. Post-exposure prophylaxis has not been shown to be effective for mumps."

While mumps usually is a self-limiting infection, reported complications in Iowa include orchitis (inflammation of the testes), meningitis, encephalitis, and deafness. There have been no reported deaths, but 55 people in Iowa have been hospitalized with complications of mumps infection, she said. With regard to hospitalized cases, mumps is transmitted by contact with virus-containing respiratory secretions, including saliva. The portals of entry are the nose and mouth. In addition to standard precautions, patients with clinical signs and symptoms of mumps illness should be cared for using droplet precautions. Droplet precautions should be maintained for nine days after onset of parotitis (swelling of the salivary glands), the CDC recommends.

The infecting agent in the U.S. outbreak is the mumps G genotype, the same strain that has caused a huge outbreak in the United Kingdom that has reached some 80,000 cases. "This is the same genotype, but it is not an uncommon genotype globally," Seward said. "As yet, we do not have an official source for the introduction [of the outbreak strain]."

Alarming case count in the twice-immunized

In Iowa, 51% of mumps cases had a history of two doses of vaccine, 12% one dose and 6% were unvaccinated. The vaccine status of 31% of the cases there is unknown. One dose of MMR (mumps, measles, rubella) vaccine has about 80% effectiveness, with two doses raising that protective effect against mumps to the 90% range. Questions have been raised about the vaccine match with the virus, particularly since half of the cases in Iowa had received two doses.

"The vaccine works against this strain," Seward emphasized. "Why are we seeing cases in two dose vaccines? Most of those are college students. This outbreak got started on college campuses. There is a great potential for transmission on the college campus setting. They are in very close quarters with lots of mixing. College students get in cars and go places and don't necessarily stay in their room and isolate themselves when they feel sick. And two doses is [only] 90% or so effective, so we can expect some failures."

The CDC is contacting college associations to get the word out, hoping many students can be immunized for mumps over the summer months. Two doses of MMR vaccine are recommended for students attending colleges and other post-high school institutions. "We have been working very closely with the American College Health Association," Seward said. "We issued a joint statement with them early in the outbreak. They are about to send a letter out signed by [CDC director] Dr. [Julie] Gerberding and their president to all of the college members to encourage vaccination of all college students over the summer break."

Colleges generally have less rigorous immunization requirements than public schools, where little transmission is occurring in part due to two-dose mumps vaccine requirements in every state, she said. "The epidemiology of the outbreak shows by far the highest age-specific incidence in those 18 to 24 years, with a median age of 22," Seward said.

If there is a public health lesson to be learned from the situation, it can be traced to a "discrepancy between policy and evidence of immunity," she said. Previous guidelines aimed primarily at eliminating measles required only one dose of MMR as evidence of mumps immunity. "The HICPAC/ACIP 1997 joint statement stated that immunity to mumps is 'highly desirable' but that was a weaker recommendation than for measles and rubella, where [it was stated] they should be immune," Seward said. "And in the ACIP 1998 statement there was no mention at all in the health care worker section of the importance of mumps immunity. [The statement] had a recommendation of just one [vaccine] dose."

The mumps outbreaks in the late 1980s revealed that one dose of vaccine will not confer sufficient herd immunity to eliminate a level of endemic transmission, she noted. "Had we had not the two-dose recommendation for measles — which was implemented well in schools — I think we would still have continued to see mumps outbreaks," she said. "When we got that recommendation, mumps went away — until this year."

Reference

  1. Centers for Disease Control and Prevention. Notice to Readers: Updated Recommendations of the Advisory Committee on Immunization Practices (ACIP) for the Control and Elimination of Mumps. MMWR June 1, 2006 (Early Release); on the web at: www.cdc.gov/mmwr/preview/mmwrhtml/mm55e601a1.htm.
  2. Wharton M, Cochi SL, Hutcheson RH, et al. Mumps transmission in hospitals. Arch Intern Med 1990; 150:47-49.