Unprotected People Reports: Mumps
Mumps Outbreak at a Summer Camp Demonstrates the Need for Vigilance Against All Vaccine-Preventable Diseases
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|The Immunization Action Coalition (IAC)
publishes articles about people who have suffered or died from
vaccine-preventable diseases and periodically devotes an IAC Express issue
to such an article. This is the 83rd in our series.
|This report describes an outbreak of mumps in a camp setting where the virus
likely was introduced by an unvaccinated counselor from the United Kingdom,
where an epidemic of mumps was ongoing. The outbreak resulted from a
combination of delay in diagnosis of mumps and failure to report the cluster
of illnesses in a timely manner, in addition to close contact among camp
|With the decrease in mumps incidence in the United States, healthcare
providers have become less likely to suspect mumps in patients with
parotitis. In this camp outbreak, although patients were evaluated by
multiple healthcare providers, including camp and hospital physicians,
parotitis was not recognized as mumps until well into the outbreak.
Providers, parents, and child care and school staff members need to be aware
of mumps signs and symptoms, potential complications, and communicability
and the need to suspect mumps regardless of patient vaccination status.
|A second lesson from this outbreak is the need for organizations assigning
foreign staff to U.S. camps to begin revising their admission requirements
to include immunity to vaccine-preventable diseases such as mumps.
|CDC published "Mumps Outbreak at a Summer Camp—New York, 2005" in the
February 24 issue of MMWR. It was reported by K. Henry, Sullivan County
Health Department; L. Pollock, MSN, C. Schulte, D. Blog, MD, P. Smith, MD,
New York State Department of Health; G. Dayan, MD, National Immunization
Program; J. Schaffzin, MD, EIS Officer, CDC. The findings in the report are
based, in part, on contributions from staff of the New York State Department
of Health Immunization Program; and from C. LeBaron, MD, National
Immunization Program, and L. Lowe and N. Williams, National Center for
Infectious Diseases, CDC. It is reprinted below in its entirety, excluding
|On July 26, 2005, the Sullivan County Health Department (SCHD) and the New
York State Department of Health (NYSDOH) were notified of a cluster of cases
of parotitis among campers and staff members at a summer camp. An
investigation conducted by NYSDOH identified 31 cases of mumps, likely
introduced by a camp counselor who had traveled from the United Kingdom (UK)
and had not been vaccinated for mumps. This report summarizes the results of
the subsequent investigation by NYSDOH, which determined that, even in a
population with 96% vaccination coverage, as was the case with participants
in the summer camp, a mumps outbreak can result from exposure to virus
imported from a country with an ongoing mumps epidemic.
Camp was in session during June 28August 18. A case of mumps was defined as
unilateral or bilateral parotitis of [more than] 2 days' duration with no
other apparent cause in a camper or staff member who was examined during
June 30September 1, 2005. Among 541 campers and staff members, 31 cases of
mumps were identified (attack rate: 5.7%), with illness onsets during June
30August 9. The index patient was a man aged 20 years who resided in the UK
and who had not been vaccinated for mumps. The man came to the United States
on June 19 to work as a counselor at the camp; on June 30, he had left-sided
parotitis, sore throat, and a low-grade fever. However, mumps was not
considered as a diagnosis by healthcare staff members at the infirmary.
The patient was not isolated and continued to work among the camp
population. During July 1523, a total of 25 additional cases of parotitis
were identified, consistent with exposure beginning June 28. However, the
diagnosis of mumps was not made by members of the healthcare staff at the
infirmary or by community healthcare providers for any patient with
parotitis until July 24. SCHD and NYSDOH were alerted to a possible outbreak
on July 26, and diagnosis of mumps for the first 23 (74%) cases was made via
retrospective chart review by NYSDOH on July 27. At that time, five (16%)
patients were either symptomatic or in isolation. Subsequently, an
additional three (10%) cases were identified, beginning on August 2.
Of the 31 mumps cases identified, 17 (55%) were in females. All patients had
parotitis, 24 (77%) had jaw pain, and eight (26%) had bilateral disease.
Four male patients had unilateral orchitis; all recovered spontaneously.
Specimens for serology and viral culture/nucleic acid detection (i.e.,
nasopharyngeal swabs and urine) were obtained from six patients. All six
serologic specimens tested positive for mumps-specific IgM; however, no
virus was successfully amplified or cultured from any clinical specimen.
Twelve (39%) of the 31 mumps cases were among campers. All were U.S.
residents aged 1015 years who had been vaccinated with 2 doses of measles,
mumps, and rubella (MMR) vaccine after the first birthday. Nineteen (61%) of
the mumps cases were among staff members; of these, nine (47%) were UK
residents, five (26%) were U.S. residents, three (16%) were residents of
Australia, and two (11%) were residents of Germany. Staff members with mumps
ranged in age from 19 to 41 years (median: 21 years). Of the 17 staff
members with mumps for whom vaccination history could be obtained by
vaccination or medical record, nine (53%) had not been vaccinated for mumps,
four (24%) had been vaccinated with 1 dose, and four (24%) had been
vaccinated with 2 doses of a mumps-containing vaccine. Symptoms, illness
duration, and complications (e.g., orchitis) did not differ substantially
between vaccinated and unvaccinated patients.
Outbreak-control measures were instituted at the camp immediately after SCHD
and NYSDOH were notified on July 26. Persons exhibiting signs or symptoms of
mumps were isolated from other campers and staff members for 9 days after
onset of symptoms. A total of 513 persons who were neither known to have
mumps nor symptomatic for mumps were quarantined to the grounds of the camp;
these persons were not permitted to enter or leave the camp until their
mumps immunity status had been verified. Mumps immunity was assessed in
accordance with Advisory Committee on Immunization Practices (ACIP) criteria
as follows: (1) birth before 1957, (2) history of physician-diagnosed mumps
before arriving at camp, (3) laboratory evidence of mumps immunity (i.e.,
positive for mumps-specific IgG), or (4) receipt of 1 dose of a
mumps-containing vaccine on or after the first birthday, as documented by a
healthcare provider. Twenty persons who could not verify their vaccination
status and did not meet any other immunity criteria had their sera tested
for mumps-specific IgG.
A total of 73 persons without immunity or with a record of 1 dose of
mumps-containing vaccine were administered MMR vaccine. Mumps information
was provided to camp personnel, and alerts were distributed to healthcare
providers statewide. Letters from NYSDOH, written in collaboration with the
camp operators, were sent to the parents of campers and directors of other
New York camps. After August 9, 2005, no further reports of mumps disease
were received at the camp, in the county where the camp was located, or in
any U.S. counties of origin for campers and staff members.
Mumps generally is a mild and self-limited viral infection; an estimated
15%20% of infections are asymptomatic. However, infections occasionally can
lead to serious complications, with or without parotitis. Meningitis occurs
in an estimated 15% of cases, of which a small percentage can progress to
encephalitis and permanent central nervous system sequelae; pancreatitis is
observed in approximately 4% of cases and sensorineural deafness in an
estimated one in 20,000 cases. First-trimester mumps infection in pregnant
women is associated with a 25% incidence of spontaneous abortion. In
addition, mumps causes orchitis in approximately 40% of postpubertal males,
with infertility as a rare consequence. The number of mumps cases reported
annually in the United States ranged from 231 to 277 cases during 20012005.
However, mumps remains endemic in many countries throughout the world, and
mumps vaccine is used in only 57% of World Health Organization
member-countries, predominantly in countries with more developed economies.
Mumps vaccine was first licensed in the United States in 1967; vaccination
with at least 1 dose of mumps-containing vaccine has been required for
school entry in New York since 1986. MMR vaccination coverage in the United
States has been estimated at [more than] 90% among children aged 1935
months since 1994. During 20042005, estimates of immunity to mumps in New
York, according to ACIP criteria, were 96% in schools and 98% in
Previous investigations of mumps outbreaks reported similar clinical
symptoms among vaccinated and unvaccinated patients. With the decrease in
mumps incidence in the United States, healthcare providers have become less
likely to suspect mumps in patients with parotitis. In the camp outbreak,
although patients were evaluated by multiple healthcare providers, including
camp and hospital physicians, parotitis was not recognized as mumps until
well into the outbreak. Providers, parents, and child-care and school staff
members need to be aware of mumps signs and symptoms, potential
complications, and communicability and the need to suspect mumps regardless
of patient vaccination status. In addition, given the low prevalence of
mumps in the U.S. population, laboratory confirmation should be encouraged
to diagnose mumps accurately.
In the camp outbreak, mumps likely was introduced by an unvaccinated
counselor who traveled from the UK, where an epidemic of mumps was ongoing,
with 56,390 notified cases reported during 2005 in England and Wales. The
likelihood of disease in U.S. residents as a result of imported virus from
areas with mumps epidemics remains high. Vaccination of counselors who will
be working in summer camps is recommended, particularly because mumps
vaccine effectiveness can be [less than] 85% in outbreak settings. As a
result of this outbreak, agencies involved in assigning foreign staff to
U.S. camps and organizations of camp administrators have begun revising
their admission requirements to include immunity to vaccine-preventable
diseases such as mumps.
The outbreak described in this report likely resulted from a combination of
delay in diagnosis of mumps and failure to report the cluster of illnesses
in a timely manner, in addition to close contact and social mixing among
camp participants. Controlling the outbreak resulted in a substantial burden
on the camp and its staff, including cancellation of activities and likely
loss of revenue. Previous mumps outbreaks also have carried substantial
burden, particularly with respect to costs associated with school
absenteeism. To prevent large outbreaks of mumps in their communities, U.S.
healthcare providers should suspect mumps independent of vaccination
history, diagnose mumps by using laboratory testing, and report mumps
immediately to local health authorities.
|2/27/06 • REPORT #83
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Unprotected People Reports for the purpose of making them available
for our readers' review. We have not verified the content of this