1.6 The clinical description of rubella and congenital rubella syndrome

The clinical diagnosis of rubella (postnatal rubella, German measles) is unreliable because there are many other causes of rash that mimic rubella infection. In addition, many cases go unrecognized or index cases may be missed since up to 50% of rubella infections are subclinical. While rubella virus causes a mild febrile rash illness in children, maternal infection with rubella can have serious consequences for the developing foetus. During the first 11 weeks of gestation, there is a very high risk (90%) that the child will be born with congenital rubella syndrome (CRS) [22].

The average incubation period for rubella is 14 days but can range from 12–23 days. In adolescents and adults, a short prodromal phase (1–5 days) occurs before the rash appears in. In children, prodromal symptoms are rare, and a rash is usually the first manifestation. The prodrome consists of a low-grade fever, malaise and mild conjunctivitis. Other symptoms may include headache, anorexia, coryza, sore throat, and cough. Enlargement of the lymph nodes (lymphadenopathy) occurs from 5–10 days before the onset of the rash. At approximately 14–17 days after infection, a maculopapular rash (a pink skin rash of discrete spots) develops. The rash starts on the face and neck, progresses down the trunk to the extremities and lasts about 3 days. The rash is much fainter than that seen in measles and is occasionally pruritic. Refer to Figure 1.5, The relationship between clinical signs, virus isolation and serological markers of postnatal rubella infection.

Although these symptoms are not specific to rubella, lymphadenopathy may be more pronounced and last longer (several weeks) with rubella than with other exanthematic diseases, such as measles. Joint pain and temporary arthritis, which are uncommon in children, occurs in approximately 70% of adults. Other complications of rubella are thrombocytopenia (1 in 3,000 cases) and post infectious encephalitis, which occurs in about 1 in 6,000 cases of rubella [23,24].

A rubella infection during the first trimester of pregnancy can cause miscarriage, stillbirth, or the birth of a child with CRS. Common manifestations of CRS are ocular defects including cataracts, deafness, congenital heart disease, and developmental delay. The list of possible defects is extensive since the rubella virus can affect any of the organs of the developing foetus. The severity and nature of these defects depend on the gestational age of the foetus at the time of infection. Infants with CRS usually present with more than one sign or symptom consistent with congenital rubella infection. However, infants may present with a single manifestation of CRS, deafness or hearing impairment being the most common defect [23,24].

When maternal infection occurs after 18 weeks of gestation, the risk of CRS is much lower. However, the newborn may still have a congenital rubella infection (CRI). A congenital rubella infection (CRI) applies to all infants confirmed with rubella infection, with or without CRS [20]. If manifestations of CRS are not present, the infant is diagnosed as having CRI only. However, some effects of foetal rubella infection may not manifest for several years.

Additional information regarding rubella and CRS surveillance can be accessed online, including the document, Introducing rubella vaccine into national immunization programmes: a step-by-step guide [25].