CONGENITAL RUBELLA

Gregg, in 1941, 5 was the first to record the devastating effects of rubella infection in the fetus and to describe the congenital rubella syndrome. Approximately 50 percent of infants who acquire rubella during the first trimester of intrauterine life will show clinical signs of damage from the virus. The earlier the infection, the more severe the fetal damage. In such infants, multiple congenital defects include low birth weight, microcephaly with mental retardation, cataracts, nerve deafness, and congenital heart disease (usually patent ductus arteriosus or ventricular septal defect). Following completion of organ development in the fetus, infection with rubella may produce a variable clinical picture, which may include hepatitis, splenomegaly, pneumonitis, myocarditis, encephalitis, and osteomyelitis. When the bone marrow is affected, the infant may be born with thrombocytopenia and bleeding into the skin, producing a striking picture of petechiae and ecchymoses given the colorful term “blueberry muffin baby.” In congenital rubella, a retinopathy consisting of a diffuse deposit of black pigmentation is commonly found.

Diagnosis

Infants with congenital rubella may be chronically infected for many months. Virus can be cultured from the nasopharynx, urine, CSF, and even the lens of infants with congenital cataract. As time passes, the amount of virus shed in the nasopharynx and urine gradually declines and disappears. Approximately 85 percent of infants infected in utero will excrete virus in the first month of life; 1 to 3 percent continue to excrete virus in the second year of life. The large amounts of virus from congenitally infected infants are very hazardous to pregnant women working with such infants who may be susceptible to infection. The infant with congenital infection will usually have elevation of IgM as a result of antibody produced by the infant itself, together with elevated IgG caused by passive transfer of antibodies in the maternal blood. IgG traverses the placenta, in contrast to IgM, which does not. The IgG antibodies disappear over the first few months of life. Passively acquired IgG by the fetus from an immune mother may explain the rarity of acquired rubella in early infancy. The antibodies against rubella consist of neutralizing, complement-fixing, and hemagglutination-inhibition antibodies. Neutralizing and hemagglutination-inhibition antibodies usually persist for life. The hemagglutination-inhibition antibodies are easily and quickly measured and serve to determine whether a recent infection can be attributed to rubella by an increase in titer in the convalescent period over the titer in the acute stage. A fourfold increase or more is considered diagnostic of the infection. Testing for these antibodies also enables the physician to determine whether a woman of childbearing age is immune or susceptible to German measles.

More sensitive tests—latex agglutination, fluorescence immunoassay, passive hemagglutination, hemolysis in gel, and enzyme immunoassay—are now available.

IMMUNITY AND IMMUNIZATION

Lifelong immunity usually follows an attack of rubella. Reinfection can occur but is usually not accompanied by clinical signs and symptoms. A rise in antibody level can occur; viremia from subclinical reinfection is very rare. Thus, congenital rubella is very unlikely in an infant whose mother has had an attack of rubella in the past and acquires a reinfection during pregnancy. In these instances, evaluation of fetal blood obtained by cordocentesis for specific rubella IgM antibodies or for evaluation by newer techniques using polymerase chain reaction (PCR) may help to confirm a diagnosis of fetal infection. 6 , 7 The availability of rubella vaccine 8 , 9 and its widespread use has markedly reduced the frequency of congenital infection.

In the United States, rubella vaccine is usually given together with mumps and measles vaccines in a single injection [mumps, measles, rubella (MMR)] at the age of 12 to 15 months and again at school entry (4 to 6 years of age).

Recommendations have been that rubella vaccine should not be given to a pregnant woman. Recent studies indicate that no cases of congenital rubella syndrome were seen among infants born to women who had been inadvertently vaccinated against rubella within 3 months of or early in pregnancy. Based upon this evidence the recommendation now is that pregnancy should be avoided for 28 days rather than 3 months following immunization. 10 Asymptomatic infections have occurred, but as noted, no cases of congenital defects have been documented. Interruption of pregnancy is not indicated.

The child or adult to whom rubella vaccine is administered does not shed sufficient virus to infect susceptible individuals in close contact. As a result, it is safe to immunize children in a family in which the mother is pregnant.