Epidemiology
The causative agent of rubella, the rubella virus, belongs to the family of Togaviridae.
Rubella has a worldwide distribution with seasonal peaks during spring and summer. Infection is uncommon in preschool children, but outbreaks involving school children and young adults living in institutions are common. In countries where vaccination has been introduced the epidemiology of rubella has changed. The incidence of rubella could significantly be reduced in these countries.

Mode of transmission: by droplet from person to person
by direct contact with respiratory secretions

Immune response and clinical features
Postnatal infections run a relatively harmless course with little or no fever; in children the disease is usually inapparent. In contrast, primary rubella infections in the early stages of pregnancy carry a high risk of foetal damage or multiple defects.

Rubella infection has an incubation period of 10-21 days, after which a rash and lymphadenopathy may appear. Further clinical features are fever and arthralgia.

Maternal primary rubella infection in the first trimester of pregnancy almost invariably results in foetal infection and may result in Congenital Rubella Syndrome (CRS) with characteristic malformations of heart, eye and ear.

Rubella specific IgG and IgM develop rapidly after onset of rash.
IgM usually appears within 4 days of onset of rash and persists for 6 to 12 weeks. IgG normally persists for life.

Diagnosis
The clinical diagnosis of rubella is unreliable. Infection may be inapparent in up to 25% of cases or the rash may result from an infection with another virus (Parvovirus B19 or enteroviruses) Serological methods are the mainstay of routine diagnosis

Investigation of acute cases
The serological diagnosis of acute rubella infections is usually based on the detection of rubella-specific antibodies (IgG and IgM). The IgG tests used for this purpose should be quantitative and calibrated against the WHO standard.

Assessment of immune status
Quantitative rubella IgG determinations are assuming an increasingly important place in the assessment of immune status. IgM antibodies are evaluated by means of index readings.

Diagnostic investigation during pregnancy
The serious consequences of a primary infection occurring in a sero-negative woman, makes rubella testing an essential element of routine antenatal care.
In the case of suspected rubella infection in early pregnancy, interpretation of serological findings focuses on identification of a primary infection, as such cases demand appropriate precautionary measures or therapeutic intervention.

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