Measles is transmitted by direct contact with infectious droplets or, less commonly, by airborne spread. Measles is one of the most highly communicable of all infectious diseases, with an approximate basic reproductive number of 12–18 in developed countries2 (see section 1.1.1). There is a prodromal phase of two to four days with fever, conjunctivitis, coryza and Koplik’s spots on the buccal mucosa. The characteristic maculopapular rash appears first behind the ears on the third to seventh day, spreads over three to four days from the head and face, over the trunk to the extremities. It lasts for up to one week. The patient is most unwell during the ﬁrst day or two after the appearance of the rash.
The incubation period is about 10 days, but may be 7 to 18 days from exposure to onset of fever. It may be longer in those given immunoglobulin after exposure. Measles is highly infectious from five days before to five days after rash onset, counting the day of rash onset as day one. Complications are common, occurring in 10 percent of cases (see Table 11.1 in section 11.7.2), and include otitis media, pneumonia, croup and diarrhoea. Encephalitis has been reported in 1 in every 1000 cases, of whom some 15 percent die and a further 25–35 percent are left with permanent neurological damage. Other complications of measles include bronchiolitis, sinusitis, myocarditis, corneal ulceration, mesenteric adenitis, hepatitis and immune thrombocytopenic purpura (ITP or thrombocytopenia).
Sub-acute sclerosing panencephalitis (SSPE), a rare degenerative central nervous system disease resulting from persistent measles virus infection, is fatal. SSPE typically occurs 7 to 10 years after wild-type measles virus infection.3 This complication has virtually disappeared where there is widespread measles immunisation.
The case fatality rate for reported cases of measles in the US is 1–3 per 1000. Measles is particularly severe in the malnourished and in patients with defective cell-mediated immunity, who may develop giant cell pneumonia or encephalitis without evidence of rash, and have a much higher case fatality rate. Measles during pregnancy can cause miscarriage, stillbirth and preterm delivery.1
Measles is also serious in healthy children: over half of all the children who died from measles in the UK between 1970 and 1983 were previously healthy.4 No other conditions were reported as contributing to the death of seven people who died from measles in the 1991 New Zealand epidemic.