Infection: Measles; rubeola
- Highly contagious vaccine-preventable viral illness, capable of causing severe disease.
- Rash is generalised, but starts on the head and neck and spreads downwards.
- Measles is very unlikely in someone with a history of two doses of MMR vaccine, or who was born before 1969.
Did you know?
- Measles is unlikely if the rash is not accompanied by at least one of: cough, coryza, conjunctivitis, or Koplik’s spots, in addition to fever at time of rash onset.
- Children with measles are typically still miserable and have fever at the time of rash onset. This differs from other common causes of childhood rash illness such as roseola, where rash onset coincides with the child looking and feeling much better and fever resolving.
Who should I test?
This varies depending on current epidemiology. Consider testing for measles in those presenting with compatible symptoms, especially if possible exposure, or if unvaccinated and born after 1969. If in doubt discuss with a clinical microbiologist or public health.
Test of choice:
Request Measles PCR
Viral nasopharyngeal or throat swab for measles PCR (RNA)
- Urine may also be sent for PCR, but the above swabs are preferred
- Excellent sensitivity – a negative result on a well-collected sample within or before the first 3 days of rash makes the diagnosis very unlikely. Beyond day 3 the sensitivity drops.
- Excellent specificity – a positive result confirms the diagnosis (unless recent vaccination has occurred)
Measles serology (IgM and IgG) is not the preferred method, but is used in some situations.
- If PCR testing within the first 3 days of rash is not possible then serology should be requested in addition to PCR.
- Measles IgM usually appears around day 3 of rash
- A negative result beyond day 3 makes the diagnosis less likely, however a positive result does not necessarily confirm infection, as cross-reactions with other illnesses can occur.
- Measles IgG usually appears around day 7 of rash
- A positive IgG, with a negative IgM within the first few days of rash therefore suggests prior immunity and makes measles unlikely.
- Conversion from IgG negative to positive between acute and convalescent (10-14 days later) blood samples confirms measles.
Tests to avoid/specialist tests:
Viral swabs of the rash for PCR
- These have limited sensitivity for detection of measles so are not recommended.
Suspicion of measles should be notified immediately to public health
- If there is sufficient suspicion to test, then public health must be notified.
People with suspected measles should avoid waiting rooms, laboratory collection centres, or other areas where they could expose others to possible infection.