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Volume 3 No 14; 9 April 2009

Continued increase in mumps in universities 2008/2009

As reported previously [1], the number of mumps cases notified in England and Wales, increased in early 2009 and has continued to increase during March (figure 1). Outbreaks have been reported from several universities and colleges. A similar increase has been reported from the Republic of Ireland [2].

A large epidemic of mumps affecting university students first occurred in the academic year 2004/5 [3] and continued into 2005/6, declining in 2006/7 and 2007/8. During the final quarter of 2008, 695 cases of mumps were confirmed compared to 447 in the previous quarter [4]. So far in 2009, 998 cases of mumps with onset in January or February have been confirmed mumps IgM or RNA positive in England and Wales. This compares to 322, 274, and 1173 cases in the same periods of 2008, 2007, and 2006 respectively. During 2009, cases have been confirmed in all English regions and Wales with high numbers from the South West (204), South East (180), and North West (162) regions. For the remaining regions the number of cases confirmed was as follows: Yorkshire and Humberside (115), London (86), East of England (81), West Midlands (64), East Midlands (48), North East (30), and Wales (27). The genotype currently circulating is a G5, the same strain that has been circulating over the past five years and responsible for outbreaks in other parts of Europe [5,6].

Figure 1: Five week moving average of mumps notifications, England and Wales 2003-2009

 

Reason for the increase

The previous epidemic was attributed to a cohort of young adults, born between 1981 and 1990, who were at increased risk of mumps. These individuals were born before the implementation of the routine two dose MMR programme and had therefore either received no MMR vaccine, or only one dose. As control of mumps was excellent after 1990, this group remained susceptible until they entered the university or college setting, when transmission of mumps was facilitated. During 2008, 1,403 (57%) of the confirmed cases were in those born between 1981 and 1990 (figure 2).

Figure 2: Confirmed mumps cases by year of birth, 2008

Despite this clear picture, the reason why the numbers of cases have increased in this academic year, after remaining lower in both 2006/7 and 2007/8 is not entirely clear. One explanation may be that, since the widespread transmission in 2005/6, three new cohorts of students have entered college and therefore another susceptible pool has been re-established in this setting.

In the previous epidemic, although the vaccinated cohorts were largely protected from mumps, cases were confirmed in vaccinated individuals. By the 2008/9 academic year, most students would have been eligible for one or two doses of MMR, and so a higher proportion of vaccine failures are expected amongst the cases. Initial reports are consistent with this observation.

In 2004-5, analysis of protection from vaccination showed that, although individual protection from vaccination was high, there was evidence of declining protection over time, particularly in those who had only received one dose of vaccine [7]. Investigations during university outbreaks in the United States, where vaccine coverage for two doses has been in place for longer, also suggested that waning protection may have contributed [8]. Secondary vaccine failure may therefore also explain a proportion of cases.

Surveillance and control

Continued surveillance, including confirmation of the diagnosis, is important for ensuring accurate epidemiological data. In persons who have been previously vaccinated, the serological diagnosis of mumps can be difficult as the IgM response may be delayed and reach lower levels. For rapid diagnosis, an oral fluid taken in the first 14 days of illness is preferred as this can be tested for both IgM and viral RNA. If this is not possible then parallel serum and throat swab or paired serum samples can be collected.

In 2005 and 2006, the incident team for the national mumps outbreak recommended that the priorities were to ensure that systems were in place to ensure that those entering university were fully vaccinated with MMR in the future. This included ensuring that pupils attending for the Year 10 booster and university entrants from 2005 onwards had received two doses of MMR.

The team also concluded that university vaccination campaigns in particular are likely to achieve low uptake and are unlikely to stop outbreaks. The offer of individual vaccination, however, should be available to students who are unvaccinated or have received only one dose of MMR Approaches being taken in individual universities this year have included using text messaging and university computer networks to alert students to these recommendations.

References

1. HPA. Mumps increase in university students, Health Protection Report [serial online] 2009; 3(10): News. Available at http://www.hpa.org.uk/hpr/archives/2009/news1009.htm#mumps.

2. Continued increase in mumps cases in 2009. Health Protection Surveillance Centre (Republic of Ireland). [online] [10 March 2009] http://www.hpsc.ie/hpsc/News/MainBody,3484,en.html.

3. Savage E, Ramsay M, White J, Beard S, Lawson H, Hunjan R, et al. Mumps outbreaks across England and Wales in 2004: observational study. BMJ. 2005 14; 330(7500):1119-20.

4. HPA. Laboratory confirmed cases of mumps, England and Wales: October to December 2008. Health Protection Report [serial online] 2009; 3(14)news.http://www.hpa.org.uk/hpr/infections/immunisation.htm.

5. Cui A, Myers R, Xu W, Jin L.. Analysis of the genetic variability of the mumps SH gene in viruses circulating in the UK between 1996 and 2005. Infect Genet Evol. 2009; 9(1):71-80

6. Mumps outbreak among the military in Luxembourg in 2008: epidemiology and evaluation of control measures. Mossong J, Bonert C, Weicherding P, Opp M, Reichert P, Even J, Schneider F. Euro Surveill [serial online] 2009 19; 14(7). pii: 19121

7. Cohen C, White JM, Savage EJ, Glynn JR, Choi Y, Andrews N, et al. Vaccine effectiveness estimates, 2004-2005 mumps outbreak, England. Emerg Infect Dis 2007 Jan;13(1):12-7.

8. Date AA, Kyaw MH, Rue AM, Klahn J, Obrecht L, Krohn T, et al. Long-term persistence of mumps antibody after receipt of 2 measles-mumps-rubella (MMR) vaccinations and antibody response after a third MMR vaccination among a university population. J Infect Dis. 2008 15; 197(12): 1662-8.

Ongoing investigation into reptile associated salmonella infections

In December 2008, the Health Protection Agency, Centre for Infections detected a gradual but sustained increase in a new phage type of Salmonella Typhimurium, designated definitive type 191a (DT 191a). Most isolates received at the Laboratory of Gastrointestinal Pathogens (LGP) were resistant to the antimicrobial tetracycline. A working hypothesis was defined based on responses from 10 interviewed cases who had been ill in November and December and a case control study launched using cases of confirmed S. Typhimurium DT 191a, with resistance to tetracycline, reported from LGP after the 1 January 2009. The hypothesis in the study was that infection with Typhimurium DT 191a was associated with exposure to reptiles.

The Centre for Infections (CfI) interviewed 21 cases and 18 controls for the study. Controls were defined as non travel-related Salmonella Enteritidis infections reported to CfI in the same time period as the cases. Of the cases interviewed, the majority owned or had contact with reptiles, especially snakes. Results from the study indicate that cases who had exposure to pet reptiles were more likely to have been ill with Salmonella Typhimurium DT 191a than those who had no reptile contact (OR 16.82; P = 0.001; 95%; CI 2.78 - ∞). In addition, most cases who reported contact with snakes also reported that the pets were fed with frozen mice.

Reports of this serotype continue to be received at LGP. To date, 110 cases with resistance to tetracycline have been received since August 2008. Cases are distributed across England, Wales, Northern Ireland and the Republic of Ireland, with 49 females and 61 males. The cases range in age from two months to 69 years with a median of nine and mean of 15 years. Thirty-five per cent of the cases are under five years of age, and 67% (74) cases under 18 (table 1). The Scottish Salmonella, Shigella and Clostridium Difficile Laboratory has also reported the same salmonella from approximately 20 cases in the past three months, and also two corn snakes, belonging to cases reporting infection. A similar association between corn snakes and frozen feeder mice has been noted.

Further environmental investigations to determine the source of infections are underway.

Table 1. Age and gender distribution of tetracycline-resistant S. Typhimurium DT 191a cases (2008- 2009)

Age group

Female

Male

Total (%)

2000-2007 mean % (all salmonella)

0-4 yrs

18

21

39 (35.4)

14.8

5-9 yrs

7

10

17 (15.4)

6.5

10-19 yrs

11

9

20 (18.2)

9.8

20-29 yrs

4

9

13 (11.8)

14.9

30-39 yrs

3

4

7 (6.4)

13.7

40-49 yrs

3

4

7 (6.4)

12.4

50-59 yrs

1

3

4 (3.6)

11.0

60-69 yrs

2

-

2 (1.8)

6.9

≥70 yrs

-

-

-

6.5

 Unknown

-

1

1 (0.9)

3.3

Total

49

61

110