“Mirror mirror on the wall, who is the most infectious of them all?”, I asked. The mirror said nothing, because, well, it’s a mirror.

R nought (R0) is an estimate of the average number of secondary infections produced by one infected individual in a completely susceptible population. It is a measure of transmissibility. The 1918 flu epidemic, estimated to have killed 50 million people, had an R0 of 1.5 to 3.8.^1,2  Zika virus, said to have interrupted Ireland’s hopes for an Olympic medal on the golf course, had an R0 of about 2.³ Poliomyelitis, which struck fear into parents before the availability of a safe vaccine, had an R0 of about 6.⁴

All of these values are minnows compared to the transmissibility of measles. While estimates vary, an R0 of 12-18 is commonly cited.⁵ Ninety per cent of non-immune individuals exposed to a case of measles will develop clinical infection.⁶ International travel increases risk of measles acquisition.

So, had the mirror responded, it would have chanted “Measles is the most infectious of them all, and next time, just Google it.  It’s very odd to talk to mirrors”.

This enormous transmissibility risk is the reason why in general practice we need to protect ourselves, our staff and our patients from measles.

As a general rule of thumb, healthcare workers born in Ireland before 1978 are considered measles-immune. For those whose immunity is uncertain, in the absence of contraindications, offering an additional MMR vaccine (or two if needed) is safe and effective. Those born in 1978 or later are considered immune if they are known to have had two doses of MMR vaccination after their first birthday, at least four weeks apart.⁷

Nationally, MMR uptake is under 90%, well below the 95% level that the WHO considers the minimum for herd immunity. There are particular geographical areas where MMR vaccine uptake is low, and particular age cohorts where serological immunity is low. Areas of particular concern include some of the border areas and north Dublin city. According to the HPSC’s sero-epidemiology unit, 18% of males currently aged 19-20 years are measles IgG seronegative.⁸

In a practice, a case of measles will cause substantial disruption. Any susceptible individual in a room occupied by a person with measles in the preceding two hours will need to be traced and offered post-exposure prophylaxis. Prophylaxis is usually by MMR vaccination, but in some cases it requires immunoglobulin. Involving public health at the earliest possible stage, by same-day notification of suspected cases, will enable prompt mitigation measures. Post-exposure prophylaxis with MMR should be carried out as soon as possible after exposure, certainly within 72 hours. Immunoglobulin should also be given as soon as possible and within six days. The best infection prevention and control measure is MMR vaccination. 

Where clinically safe to do so, suspected cases of measles should be managed over the phone. When face-to-face consultations are required, patients with suspected measles should be seen in a room that can be left vacant for two hours after the consultation. They should avoid areas used by other patients and should be managed by staff who are measles-immune. This is probably most feasible by aiming to assess such patients at the end of the day. This presents practical difficulties, but the implications of an outbreak in a practice centre present even greater challenges.  

Cough etiquette, hand hygiene and offering surgical masks to patients with acute respiratory symptoms help to minimise transmission. Use of FFP2 masks by clinical staff managing suspected cases of measles is recommended. Those suspected of measles should self-isolate at home. If hospital admission is needed, the hospital should be informed in advance of the referral of a case of suspected measles.

Test for measles by collecting oral fluid using the OraCol collection device, or a mouth/throat VTM/UTM swab if OraCol is unavailable. Where phlebotomy is possible, a serum sample should also be sent. The following information should be provided on the request form: date of rash onset; date of prodromal symptoms onset; date of sample collection; MMR vaccine history - one or two doses, including dates if possible; and referring clinician contact number (ideally a mobile number).