Rubella IgG avidity index

Rubella is an acute, contagious anthroponotic infectious disease caused by the Rubella virus, an RNA-containing virus belonging to the family Togaviridae (genus Rubivirus).

The infection is transmitted via airborne droplets. The rubella virus is contagious from one week before the onset of rash to one week after the appearance of the rash. The incubation period lasts 2–3 weeks. Approximately 30–50% of rubella cases are asymptomatic. In other cases, the clinical presentation includes fever, a short-lived maculopapular rash, lymphadenopathy, rhinorrhea, and conjunctivitis. Rubella-associated lymphadenopathy is a persistent feature of the disease and is often its only manifestation.

Rubella is particularly dangerous for pregnant women due to the risk of intrauterine fetal infection. The rate of fetal involvement depends on the gestational age at the time of infection. The earlier the maternal infection occurs, the higher the risk of fetal damage and the broader the spectrum of possible congenital abnormalities. Rubella infection during the first trimester of pregnancy is the most dangerous and leads to congenital malformations in up to 60% of cases. These may include developmental delay, visual and hearing impairments, congenital heart defects, skeletal abnormalities, cranial defects, and others. Therefore, systematic serological screening is recommended for women of reproductive age to identify at-risk groups.

Laboratory diagnosis of rubella is based on the detection of serological markers, including IgM immunoglobulins, IgG, and IgG avidity.

Specific IgG antibodies typically appear about one week after the onset of IgM antibodies; their levels rise rapidly, peak at 6–10 weeks after the onset of illness, and then gradually decline to a stable titer that may persist for life. Complete asymptomatic reinfection may be accompanied by a moderate increase in IgG levels. Detection of IgG antibodies is used to assess post-vaccination immunity (which develops 25–50 days after vaccination) and to determine a history of past infection.