Measles is a highly contagious infection caused by a morbillivirus of the paramyxovirus family. It infects nearly all susceptible people who come into contact with it (on average, within a susceptible population, 15–20 people will be infected from a single case). Once infected, the person develops lifelong immunity.

In the UK, the measles, mumps, and rubella vaccine was introduced in 1988. With coverage levels of more than 90%, notifications of measles are at very low levels.

Transmission

Measles is an airborne infection that is spread by droplets from coughing or sneezing, close personal contact, or direct contact with nasal or throat secretions.

Measles has an incubation period of about 10 days, with a further 2–4 days of prodromal symptoms (including malaise, fever, and cough) before the characteristic skin rash develops.

The person is infectious from when symptoms first appear (around four days before the rash appears) to four days after the onset of the rash.

Clinical features

Clinically typical measles is defined as presenting with the classical symptoms of cough and coryzal symptoms, and conjunctivitis, and fever of 39ºC or more without antipyretics, and maculopapular rash.

• The prodromal phase occurs 10–12 days after contracting the infection and lasts for 2–4 days before the rash becomes apparent. Symptoms include increasing fever, malaise, cough, rhinorrhoea, and conjunctivitis.
• Fever increases during the prodromal phase to around 39ºC at about the time the rash appears, and then gradually decreases.
• Koplik's spots may appear on the buccal mucosa at the end of the prodromal phase, around the same time as the rash, and disappear over the next couple of days. These consist of 2–3 mm red spots with white or blue-white centres. These are pathognomonic for measles but can easily be confused with other mouth lesions.
• The rash is erythematous and maculopapular and may become confluent as it progresses. It appears on the face and behind the ears first (when other symptoms tend to be at their most severe), before descending down the body to the trunk and limbs, and forming on the hands and feet last, over the course of about 3–4 days. The rash fades after it has been present on an area for about 5 days, with the total duration of rash being up to 1 week, after which time the person should feel better.

Differential diagnosis

Consider a different cause for the rash if the person is likely to have immunity to measles, clinical features are atypical, there is no history of contact with measles or travel to measles-endemic countries, and there are no local outbreaks.

Infections that may be misdiagnosed as measles include:

• Parvovirus B19, the virus that causes fifth disease (erythema infectiosum, also known as slapped cheek syndrome) - this is a mild self-limiting illness that, in addition to a bright red rash on the cheeks, may cause a red, lacy rash on the rest of the body which can be mistaken for measles. However, there are no Koplik's spots. Arthralgia and arthritis may occur in adults.
• Streptococcal infection (for example scarlet fever) — can cause a maculopapular rash which appears on the abdomen and spreads to the back and limbs 12–24 hours following symptom onset. Sore throat is usually a prominent symptom and cough generally is not a feature. 'Strawberry tongue' (a white coating) may be visible.
• Herpes virus type 6 (roseola infantum) — a mild illness which may be asymptomatic. Fever can last for 3–5 days after which a maculopapular rash appears (when clinical improvement has occurred).
• Rubella — typically mild and presents with a rash which is maculopapular but not confluent. The rash usually starts behind the ears and on the face, and then spreads down the body (similar to measles). However, the infection is generally mild, and if fever is present it rarely occurs after the first day of the rash. There may be postauricular and suboccipital lymphadenopathy. Koplik's spots are not visible.
• Early meningococcal disease — may present with a maculopapular rash, but becomes purpuric in later stages, and does not fade when a glass is pressed against it.
• Other causes of rash to consider that are associated with lymphadenopathy include Kawasaki disease and infectious mononucleosis.

Management

• If there is any suspicion of measles infection, immediately notify the local health protection team (HPT). Measles is a notifiable disease. Confirm the infection through laboratory investigation (but notification should not await laboratory confirmation). Ask the HPT about the need for a testing kit and the testing schedule. Usually, an oral fluid sample will be required for IgM/IgG and/or viral RNA testing.
• Seek advice from the local Health Protection Team if the person is immunosuppressed, pregnant or an infant who is 1 year of age or younger.
• Advise patients:
  • That measles is usually a self-limiting condition that will usually resolve over the course of about a week.
  • To rest, drink adequate fluids, and take paracetamol or ibuprofen for symptomatic relief.
  • To stay away from school or work for at least 4 days after the initial development of the rash (ideally until full recovery to reduce the risk of infective complications).
  • To avoid contact with susceptible people (that is, people who are not fully immunised through vaccination or natural exposure, infants, pregnant women, or immunosuppressed people).
  • To seek urgent medical advice if they develop signs of a complication of measles, for example shortness of breath, uncontrolled fever, or convulsions or altered consciousness.

Complications

Complications of measles occur in 10–20% of people in developed countries, but the number may be much higher in developing countries.

• Susceptibility to opportunistic infection is increased for several weeks after the person has recovered from measles. The reason for this is that the measles virus suppresses the reaction of the immune system to other pathogens. Secondary infections of the respiratory tract include:
  • Otitis media
  • Pneumonitis
  • Tracheobronchitis
  • Pneumonia
• Central nervous system complications include:
  • Convulsions
  • Encephalitis
  • Blindness
  • Subacute sclerosing panencephalitis (SSPE) — a rare but serious degenerative disease of the central nervous system involving seizures and a decline in motor, cognitive, and behavioural function. SSPE occurs a median of 7 years after exposure to the virus, although it may occur as late as three decades afterwards, and is invariably fatal.
• Diarrhoea and dehydration
• Complications of measles can be more severe in:
  • Adults, who are more likely to develop complications than children
  • Pregnancy, when it may result in miscarriage, premature birth, and intrauterine death and stillbirth (note: there is no evidence associating measles with congenital defects)
  • Immunocompromised people, who are at particular risk of developing severe and prolonged measles and complications such as viral pneumonitis
  • Chronically ill or malnourished children, who can experience more frequent and severe complications
  • Infants, who are more likely to require hospitalisation than older children and are at higher risk of pneumonia, otitis media, SSPE and mortality due to measles