Common Skin Infections

Rubella

Infection may be asymptomatic in up to 25%. Adults may experience prodromal symptoms of malaise and fever for a day or two before the rash but in children the onset is usually abrupt, with the appearance of the rash. The rash starts on the face as macular lesions and then spreads to the trunk and limbs. It seldom lasts for more than 3 days and may also be seen on the soft palate. There is usually pharyngitis and enlargement of the cervical, and especially the suboccipital and postauricular lymph nodes. Lymphadenopathy may be generalised and tender, may present up to a week before the rash and persist for 10-14 days after the rash. Constitutional symptoms are usually mild in children. N.B. the rash is not diagnostic of rubella as other viruses may cause the symptoms.

Clinical tip: the rash is often a very specific 'pillar box' red in colour and look for occipital lymph nodes.

It is usually benign but the following complications are recognised

• Arthralgia- rare in children but may occur in up to 50% of adult females. It usually develops as the rash subsides and persists for less than a week (occasionally longer). The most common joints affected are the finger joints, wrists, knees and ankles. The arthralgia is believed to be mediated by immune complexes but hormonal factors may play a role because in female vaccinees joint symptoms are most likely to develop within 7 days of the onset of the menstrual cycle.
• Postinfectious encephalomyelitis may develop in 1 in 5000-10,000 cases within a week of onset of the rash. It is not associated with demyelination or inflammatory damage and the prognosis is good.
• Thrombocytopenic purpura is rare.
• Primary maternal rubella infection in the first ten weeks of pregnancy results in foetal damage in up to 90% of infants. The risk of damage declines to 10-20% by 16 weeks and is rare after 16 weeks. Congenital rubella syndrome consists most commonly of a triad of cardiac abnormalities (e.g. patent ductus arteriosus, ventricular septal defect), cataracts and deafness. Other abnormalities include mental retardation, growth retardation, hepatosplenomegaly, jaundice, anaemia, thrombocytopaenic purpura and bony lesions. Any combination of defects may occur, although perceptive deafness and pigmentary retinopathy may occur alone. Infants may appear normal at birth. Rubella re-infection has a lower risk of foetal infection, approximately 8% in the first 16 weeks of pregnancy, and foetal malformations are rare. Infants with congenital rubella syndrome are highly infectious, excreting virus from their pharynx and in urine. Approximately one third will still excrete virus at 6 months of age, although this seems to be rare after the age of 2 years.

There is good immunity after both naturally acquired rubella and vaccination. However, reinfection may occur and can be asymptomatic. It is diagnosed by demonstrating a significant rise in specific anti-rubella IgG following exposure.

All pregnant women with possible rubella infection or exposure to rubella need to be investigated serologically regardless of a history of previous rubella or vaccination. Blood should be taken as soon as possible after the onset of symptoms or exposure to detect the presence of rubella specific IgG and IgM. No particular titre of antibody is indicative of present or recent infection-a further sample should be sent 7-10 days later to detect a significant rise in antibody titres. Low levels of IgM may be detected for up to 4 years following rubella vaccination and may be detected in reinfection so this result is not diagnostic of recent primary infection. A good clinical history of LMP, timing of exposure, symptoms and previous infection/ vaccination will help in the interpretation of the results. Sending a blood sample for detection of rubella IgM or a salivary swab if the case is a child should do confirmation of rubella in the index case.

The vaccine consists of live attenuated virus and is therefore not recommended in pregnancy. Susceptible women should be vaccinated after delivery. Pregnancy should be avoided for one month after rubella vaccination.

Post exposure prophylaxis with HNIG is of little value as it does not prevent infection in non-immune contacts, although it may reduce the likelihood of clinical symptoms. Its only recommended use is for when termination for confirmed rubella would be unacceptable, and it should be given soon after exposure.

Other viruses which cause rubelliform rashes and arthralgia

Parvovirus B19, enteroviruses (coxsackie A, echovirus) and some arboviruses e.g. Ross River virus.