[Medical study of cases diagnosed as rubella in adults]

In 2012, the number of rubella cases sharply increased in Japan. It continued to rise in 2013. Between October 2012 and May 2013, 10 cases of congenital rubella syndrome (CRS) were reported nationwide. This current rubella outbreak comprised mainly males who were between 20 to 39 years of age, and had not received the rubella vaccine. Data have been lacking on the clinical characteristics of adults infected with the rubella virus.

Using medical charts, we collected data from 27 patients who were diagnosed with clinically or laboratory-confirmed rubella infection at Tokyo Metropolitan Komagome Hospital from January 2012 to April 2013.

Of the 27 patients studied, their median age was 34.5 years and 70.4% were male between 21-56 years of age. For the 11 cases with known vaccination status, 9 (81.8%) occurred in persons who had not received a rubella vaccine. A total of 33.3% of the patients were hospitalized, due to persistent fever, poor oral intake, or dehydration. Major clinical symptoms were fever (96.3% of cases), lymphadenopathy (92.6%), rash (85.2%), conjunctivitis (77.8%), and headache (63.0%). The mean duration of fever was 5 days (range, 3-9). The exanthema consisted of punctate, pink maculopapules; however, the rash became confluent in 37.0%, and pigmented in 18.5% of the patients. Initial laboratory data were as follows:white cells, 3,800/microL (range: 2,000-8,300); platelets, 129,000/microL (range, 63,000 - 230,000); aspartate aminotransferase, 27IU/L (range, 16 - 49); lactase dehydrogenase, 279IU/L (range, 168-440) [all described in medians]. Rubella-specific immunoglobulin M antibodies from the serum sample obtained at the initial visit were detected in 17 cases (65.4%). Likewise, measles-specific immunoglobulin M antibodies were detected in 7 cases (26.9%), all of which were false-positive.

The clinical characteristics of rubella in adults resembled measles in some part, which may cause difficulty for physicians to differentiate between the two diseases. Vaccinating rubella-susceptible individuals now is critical to interrupt rubella virus transmission, and to prevent further CRS cases.