Mumps outbreak in Perth
The Perth metropolitan area is experiencing an outbreak of mumps, with 23 confirmed cases notified with illness onset between 25 December and mid-February, compared to 2 cases in the same period last year. No mumps cases have been notified in Western Australian residents outside Perth for more than 12 months.
With one exception, all the recent cases appear to have acquired their infections locally (see Figure 1). Direct linkages to a source have been identified for only 4 cases, suggesting that there could be many other cases in the community not being detected. This is supported by anecdotal reports of undiagnosed cases, and knowledge that around one third of people infected with mumps do not have obvious symptoms.
Two thirds of the notified cases live in the northern suburbs and most are older teenagers or young adults aged in their 20s and early 30s. Around one third of the cases have documented evidence of being partially (1 dose) or fully (2 doses) vaccinated against mumps, while one third have not been vaccinated, and there is no information for the remainder. Three cases (13%) have been hospitalised, including one with meningitis and another with orchitis.
Figure 1 – Mumps notifications in Western Australia, January 2012 to 25 February 2013, by likely place of acquisition.
Mumps became a notifiable disease in Western Australia in 1993, and excepting a large and localised outbreak in the Kimberley region in 2007–2008, the annual number of notified cases has fluctuated between a low of 7 cases in 1994 and a high of 40 cases in 2000. On a statewide basis, in the 4 years 2009–2012, an average of 1.4 cases were notified per month, around 50% of whom acquired infection overseas. Hence, the upsurge in cases since late December 2012—primarily locally acquired—is unusual.
The 2007–08 Kimberley outbreak was also very unusual in that there was clearly intense and sustained local transmission, primarily in Aboriginal residents of that region aged between 5 and 29 years, a high proportion of whom were partially or fully vaccinated.1 While 148 cases were notified in Kimberley residents between July 2007 and September 2008, only 2 cases have been reported from the Kimberley since then. The Kimberley outbreak was caused by a genotype J mumps virus, and it is thought that the mumps vaccine, which is of genotype A lineage, may not offer good protection against all strains.
Similarly, the United States, Canada and several European countries have also experienced outbreaks of mumps in recent years, characterised by high incidence in older teenagers and young adults, a high proportion of whom have been vaccinated. 1–5 Several of these outbreaks have been due to genotype G5 mumps virus, which has been identified in all three of the recent WA cases for whom typing has thus far been performed.
Resurgent mumps in the United States and Europe has been attributed to several factors, including waning immunity in young adults who were vaccinated in childhood, lack of boosting of immunity due to significantly decreased circulation of wild-type virus, and diminished serologic cross-protection due to antigenic differences between the Jeryl Lynn (genotype A) mumps vaccine strain and circulating strains, including genotype G5.1–4Mumps vaccine was introduced to the childhood immunization schedule in WA in 1981 as a single dose given at age 12 months. A second dose—as part of the combined measles-mumps-rubella (MMR) vaccine—was added to the schedule in 1994, initially at age 12 years and from 1998 at age 4–5 years. Estimates of effectiveness for 2 doses of mumps vaccine range from around 88% to 95%.1,2 Hence, even with reasonably high MMR vaccine coverage—estimated in WA for the latest quarter (September 2012) as 93% and 90% in children aged 2 years and 5 years, respectively—herd immunity may not be sufficiently high to prevent outbreaks. This would particularly affect older age groups where vaccine coverage is expected to be lower, immunity has waned and where social circumstances may facilitate transmission, such as close contact in tertiary education settings, over-crowded houses and nightclubs.2
Preferred tests and specimen collection
All persons with illnesses compatible with mumps—fever, swelling and tenderness of one or more salivary glands—should preferably be tested to verify the diagnosis, at least where there is no known linkage to a case that has already been laboratory-confirmed. Serology alone is unreliable for diagnosing mumps in people who have been previously vaccinated as many have IgG but do not mount an IgM response. Also, both IgG and IgM may be absent in very early infection in unvaccinated individuals.
Hence, it is recommended that all suspect cases have both serology (IgG and IgM) and, if parotitis is still present, that specimens are also collected for virus detection by isolation/PCR. Virus can be isolated from previously unvaccinated cases from 6 days prior to—and up to 9 days after—symptom onset but in previously vaccinated cases the PCR is usually negative after 3 days of symptoms. Specimens for PCR and/or isolation should be referred to PathWest at the QEII Medical Centre for testing.
Since PCR is not positive in all cases, those with a negative PCR should have a convalescent serum sample sent to look for a rising IgG titre. The common mumps IgG tests used by most laboratories cannot detect rising IgG, so these specimens should be referred to PathWest at the QEII Medical Centre.
Preferred specimens for PCR/isolation are buccal swabs (and/or throat swabs) collected using a sterile dry cotton-tipped swab placed into a sterile vial containing viral transport medium (VTM) (see Figure 2), as this allows testing by both PCR and culture. If VTM is not available and cannot be obtained quickly, dry swabs should be sent as these can still be used for PCR. Swabs are recommended for anyone with ongoing parotitis, but preferably within 5 days of onset.
Virus detection can also be undertaken on clean-catch urine specimens in a sterile screw-top jar, collected up to around 14 days after symptom onset. Swabs and urine specimens should be kept at refrigerator temperature (4–8 ºC), but not frozen.
Figure 2 – How to collect a buccal swab for mumps virus testing
Step 1: Massage the parotid gland (area between the cheek and teeth below the ear) for 30 seconds prior to the collection of buccal secretions. The parotid duct drains into this space near the upper rear molars.
Step 2: Swab the buccal cavity near the upper rear molars between the cheek and teeth. Using a sterile dry cotton tipped swab (plastic or metal shaft, as pictured in step 3), place between the molars and cheek and leave in place for 10 to 15 seconds.
Note: Charcoal and Gel based swabs are inappropriate for PCR and viral culture.
Step 3: Place the swab immediately into a sterile vial containing 3 mL of viral transport medium (yellow-lidded vial pictured). Break or cut shaft and seal in the vial and label with patient's name, date of collection and specimen site. Keep sample cold. Do NOT freeze.
If viral transport medium is unavailable, place dry swab back into tubing, seal and label with patient's name, date of collection and specimen site.
|Adapted from information developed by Seattle and King County Public Health (USA) (external site)|
Notification and public health response
Cases should be excluded from school, other educational settings, work, and public places where other susceptible people may be present, for 9 days after the onset of symptoms. Incompletely vaccinated close contacts should be offered MMR vaccine, although post-exposure vaccination will not always prevent infection.
All suspected or confirmed cases should be notified to the Communicable Disease Control Directorate (CDCD - Perth) or the appropriate Public Health Unit (regional areas), preferably by telephone or fax, using the standard notification form. Public Health Units will follow-up cases to investigate exposure history, facilitate testing where appropriate in liaison with the diagnosing clinician, and identify contacts who may benefit from advice or other action.
At a community-wide level, it is important that all children receive their MMR vaccinations on time, at 12 months of age and at 4 years, prior to commencing pre-school. Vaccination should also be offered opportunistically to older children and young adults who do not have documentation of having received two doses of MMR vaccine, especially prior to overseas travel. Measles, rubella and mumps viruses continue to be imported into WA by returning travellers or incoming visitors who are infected in overseas countries where these diseases remain endemic.
In the meantime, CDCD will maintain close surveillance. Any wider response, such as promoting a third dose of MMR vaccine among adolescents and young adults, either generally or in more focused settings, will be determined by how the outbreak evolves.
- Bangor-Jones RD, Dowse GK, Giele CM, van Buynder PG, Hodge MM, Whitty MM. A prolonged mumps outbreak among highly vaccinated Aboriginal people in the Kimberley region of Western Australia. MJA 2009; 191: 398–401.
- Dayan GH, Quinlisk MP, Parker AA, et al. Recent resurgence of mumps in the United States. N Engl J Med 2008; 358:1580–1589.
- Otto W, Mankertz A, Santibanez S, et al. Ongoing outbreak of mumps affecting adolescents and young adults in Bavaria, Germany, August to October 2010. Euro Surveill. 2010;15(50):pii=19748. View on the Eurosurveillance website (external site) .
- Whelan J, van Binnendijk R, Greenland K, et al. Ongoing mumps outbreak in a student population with high vaccination coverage, Netherlands, 2010. Euro Surveill. 2010;15(17):pii=19554. View on the Eurosurveillance website (external site).
- Walker J, Huc S, Sinka K, Tissington A, Oates K. Ongoing outbreak of mumps infection in Oban, Scotland, November 2010 to January 2011. Euro Surveill. 2011;16(8):pii=19803. View on the Eurosurveillance website (external site).