Background

Measles is a highly infectious viral disease which can be prevented if people are vaccinated against it. Two doses of a measles containing vaccine, included in the Measles-Mumps-Rubella (MMR) vaccine are recommended to prevent measles. The disease caused by the virus presents as a fever-rash illness, typically characterised by a high temperature, fever, cough, runny nose (coryza) and conjunctivitis. Approximately 30% of all measles cases report one or more complications. Complications are more common in children less than 5 years of age and adults 20 years of age and older. ¹

The measles virus is readily transmitted by respiratory droplets and aerosols from infected individuals to those who are non-immune. Transmission occurs from four days before rash onset (before the person realises that they have measles) until four days after rash onset. Direct face-to-face contact is not needed for transmission to occur as the virus is airborne via very small respiratory droplets when the infected person coughs or sneeze. The virus can survive in the air for up to two hours. If other people breathe the contaminated air or touch surfaces contaminated with the virus , and then touch their eyes, noses, or mouths, they can become infected. Measles is so contagious that if one person has it, 90% of the people close to that person who are not immune will also become.²

Measles outbreaks occur when non-immunised people are exposed to and become infected with measles. This exposure often occurs without the person even knowing that they have been exposed to the virus (in public settings, in health care facilities).

In this report we present preliminary data on measles epidemiology in Ireland between week 18 2016 (early May) until week 29 2016 (week ending 24/7/2016). Most cases included in this report are linked to a national outbreak that followed importation of measles from a European country where measles outbreaks were occurring and spread rapidly. A report on preliminary data from this outbreak was recently published in Eurosurveillance.³ For some cases reported during this time period it has not yet been possible to identify clear epidemiological links to other outbreak related cases (and further investigations are being done to determine if linked). Only one case (notified in week 29) is clearly not linked to the outbreak and was imported from another European country.

Methods

For this report, we extracted all measles notifications reported on  the Computerised Infectious Disease Reporting system (CIDR) between Week 18 2016- week 29 2016 (date of extraction 27/7/2016). Data are provisional for the time period under review. We describe the data by age, gender, area of residence and case classification. Cases are classified according to agreed case defintions.⁴ A possible case is defined as a person with the clinical signs and symptoms compatible with measles, a probable case is a person with clinical signs and symptoms and an epidemiological link, and a confirmed case is as any person with both  clinical and laboratory criteria (isolation of measles virus from a clinical specimen or detection of measles virus nucleic acid or measles virus specific antibody response characteristic for acute infection in serum or saliva) in the absence of recent vaccination with a measles containing vaccine. The National Virus Reference Laboratory (NVRL) undertook diagnostic testing on all confirmed cases.  Vaccination status was extracted from CIDR as reported to public health and was not routinely validated for all cases. 

Results

A total of 43 measles notifications were extracted from CIDR for weeks 18 to 29 2016 (date CIDR data extracted 27/7/2016). The first case notified during this time (week 18) reported travel from another European country during the incubation period. Subsequently a fellow passenger on the flight back to Ireland was laboratory confirmed as having measles. In the early stage of the outbreak, transmission occurred amongst non-immune contacts in a variety of community and health care settings. The number of cases peaked in week 22 when 13 cases were notified. Since then the number notified each week has been decreasing. In week 29, a traveller arrived from another European country and was diagnosed shortly after arrival with laboratory confirmed measles. (Figure 1)

Figure 1. Measles notifications, by week and case classification, weeks 18-29 2016

During this time males and females were equally affected; 36 cases were case classified as confirmed and 7 as possible; the greatest number of cases occured in the 0-4 year age group (median age 7 years, age range 3 months – 40 years). (Figure 2). The HSE area most affected was the HSE South area with 25 notifications. (Figure 3). 

Figure 2. Measles notifications, by age group and case classification, weeks 18-29 2016

Figure 3. Measles notifications by HSE area and case classification, weeks 18-29 2016

Of the 43 cases, 8 were too young for vaccination (<12 months); 29 of the 35 cases who were age eligible for vaccination were laboratory confirmed; of whom 24 (87%) never received MMR vaccine, three reported two doses of MMR, but for only one of these cases could it be verified, and two adult cases they did not know vaccination status. (Figure 4).

Figure 4. Measles notifications, by number of MMR vaccines doses, weeks 18-29 2016

Information on hospitalisation status was available for 41 cases; 16 (39%) were hospitalised; most cases hospitalised were in the 0-4 year age group, but the age groups with the greatest proportion of cases hospitalised were the 10-14 and 25-34 year age groups. (Table 1). The number of days hospitalised was reported for 10 cases (total of 43 days reported) and the median length of stay for each case was 4 days (range 2-8 days). No deaths or serious sequelae have been reported in CIDR. 

Table 1. Measles cases hospitalised by age group (and percentage of total cases), weeks 18-29 2016

Investigations and control  

Public health departments have investigated and implemented control activities upon notification of any suspected case. Cases investigated and found not to have measles were denotified (not shown in this report). Susceptible contacts identified were advised to get MMR vaccine or immunoglobulin if indicated (dependent on risk group and if within 6 days after exposure). Likely source of infection was obtained from each case where possible in order to identify others who may be at risk from similar exposures. Settings where onward transmission could occur (household settings, hospitals, GP settings, work places, schools, other community places) could occur were identified by public health investigators who then communicated with parents, families, clnicians and members of the community regarding the risk and advised them to seek medical attention/vaccination as appropriate. The NVRL undertook laboratory testing of all cases (serology, PCR and genotyping).

The National Immunisation Office and National Cold Chain distributed additional MMR vaccine supplies to those areas where the cases were occurring to meet demand. Alerts were cascaded out to clinicians via email, newsletters and direct contact by Departments of Public Health to raise awareness of the outbreak. Press and web news items were prepared by the outbreak control team to update the public about the continued measles threat as it emerged. Infection control practitioners raised awareness in health care settings to prevent measles transmission occurring.

Discussion

The measles outbreak reported in this report has had significant impact on the patients, the general public, hospitals and primary care services in the country. As a result of rigorous and timely investigations and control the outbreak is now declining. However, as we have seen in recent months, one case, if not identified or notified in time, can result in a large and widespread outbreak.

These data relating to measles during this time period under study are provisional at this time. A final report will be published once all investigations and results are completed.

Recommendations          

The best way to protect against measles is to get the MMR vaccine. All children should get MMR at 12 months of age and the second dose at 4-5 years of age. Any child who missed their scheduled MMR vaccine dose should contact their GP to get the age appropriate dose.

Most Irish born adults born since 1978 should have received measles vaccine to prevent measles as part of the national immunisation programme which started in 1985 (MMR replaced the measles only vaccine in 1988). Most adults born before 1978 will be measles immune because they were exposed to measles as children. However, as one individual in this outbreak was 40 years of age, it is possible that some adults born before 1978 may be non-immune.

All new health care workers are required to have two documented doses of MMR prior to commencing work.

People travelling overseas are also recommended to ensure that they are vaccinated if non-immune. Internationally many countries (including European countries) continue to experience measles outbreaks. Exposure to measles at airports and during air and sea travel is well documented.^5,6,7

If anyone develops measles symptoms, they should 

• Stay at home and phone their GP
• Tell the doctor or nurse that they think they might have measles
• Stop visitors coming to the house to prevent spreading the infection

Measles is a notifiable disease and GPs and hospital clinicians should immediately notify public health if they suspect someone has measles.

For more information on measles please visit HPSC website at http://www.hpsc.ie/A-Z/VaccinePreventable/Measles/

Report prepared by Dr Suzanne Cotter and Dr Sarah Gee on behalf of the Measles Outbreak Control Team*

*The authors wish to thank all members of staff in the regional HSE public health departments and the Health Protection Surveillance Centre who were involved in investigation and control measures in this ongoing outbreak. This work would not have been possible without the valuable efforts and contributions of all other members of the national outbreak control team: P Barrett, K Chaintarli, F Ryan, A Cronin, L Carlton, M MacSweeney M McDonnell¹, J Connell, R Fitzgerald, D Hamilton, M Ward, R Glynn, C Migone, A McNamara, A Clarke, A Dillon, A Breslin, A McLoone, A McKeating, B Deasy, B Cosgrove, B Corcoran, B Smyth, C Lynch, C Ó Maoldomhnaigh, F O’Donoghue, D O’Donovan, E Brabazon, E O’Connell, F O’Dea, F O’Connell, F Cooney, I Kelly, J O’Gorman, J Cuddihy, K Buckley, K Kelleher, M McIver, M Morris Downes, M Leahy, M Canny, N O’Callaghan, N Millar, N Treacy, O Hanrahan, P Kavanagh, P Flanagan, P Jennings, R Kiernan, S Doyle, A Margiotta. The authors also wish to thank Grainne Tuite and Margaret Duffy at the National Virus Reference Laboratory for assistance with genotypic analysis of the cases. They wish to thank clinical, nursing and management colleagues in local hospitals and primary care who have assisted with control measures, as well as all the affected cases and their families for their cooperation.

References

1. WHO. Measles fact sheet. Available at http://www.who.int/mediacentre/factsheets/fs286/en/
2. CDC. Transmission of measles. http://www.cdc.gov/measles/about/transmission.html
3. WE Bischoff et al. Air and Surface Detection of Measles Virus RNA in a Hospital Setting. J Infect Dis. (2015). Available at http://jid.oxfordjournals.org/content/early/2015/09/18/infdis.jiv465.full.pdf+html
4. P Barrett et al. An ongoing measles outbreak linked to a suspected imported case, Ireland, April to June 2016 http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=22522
5. ECDC. Epidemiological update: Measles on a cruise ship, 21 March 2014. http://ecdc.europa.eu/en/press/news/_layouts/forms/News_DispForm.aspx?List=8db7286c-fe2d-476c-9133-18ff4cb1b568&ID=972#sthash.TqPHtcBE.dpuf
6. Edelson PJ. Patterns of measles transmission among airplane travelers. Travel Med Infect Dis. 2012 Sep;10(5-6):230-5.
7. Muscat M. Who Gets Measles in Europe?  J Infect Dis. (2011) 204 (suppl 1): S353-S365.http://jid.oxfordjournals.org/content/204/suppl_1/S353.full