The number of adults suffering from measles has risen sharply in recent months, with a Tokyo hospital reporting about 20 such cases in the last two months, according to officials at the Health and Welfare Ministry.

Medical institutions monitoring the disease have reported to the ministry that the number of people that have contracted measles since January total about 12,000, a threefold increase over the previous 12 months, the officials said.

Many reports came from Osaka, Chiba, Saitama and Kagawa prefectures, while most of those infected were in their 20s, they said.

Of those infected with measles so far this year, some 180 were adults. This figure exceeds by three or four times the total number of adult cases in 1999.

The officials attributed the rise to the fact that only 70 percent were vaccinated against measles in the early 1990s. Almost all youths were vaccinated in earlier decades.

“It’s not wrong to say the disease is prevalent this year. I’ve heard similar stories from other hospitals (that they are treating adult measles patients),” said Kyoichi Totsuka, a professor at Tokyo Women’s Medical University Hospital’s Department of Infectious Diseases.

Totsuka said that in January, the hospital had two cases of adult measles one after another and many more since then, with some patients requiring hospitalization.

A man in his 50s contracted measles despite having had the disease as a child, he said.

Many of the patients who were reinfected with the virus had failed to be vaccinated, but there were cases in which those who were vaccinated became reinfected with the disease, he added.

Measles is generally considered a childhood disease, and those infected once usually do not contract the disease again.

“I have seen five cases of measles this week, and there is no sign that the number will fall,” said Ken Kikuchi, a lecturer at the university’s hospital.

“Women infected with the disease are more likely to miscarry or give birth prematurely,” Kikuchi said.

He said adults become susceptible to other serious diseases after contracting measles.

Measles, an acute contagious viral disease, is marked by an eruption of distinct red circular spots on the skin and a high fever.