A flulike illness, transmitted by animal urine and usually regarded as a rural threat, appears to be a common inner-city hazard, according to researchers at the Johns Hopkins School of Hygiene and Public Health.
Writing in the journal Annals of Internal Medicine, the scientists described three severe cases of leptospirosis in Baltimore and found strong evidence that the victims were infected through cuts suffered in rat-infested alleys.
A 1992 Baltimore study that revealed that many inner-city residents have developed antibodies from exposure to the bacteria.
"Leptospirosis may be the most common disease that rats carry and transmit to humans in the United States," the study said. "It's simply under-recognized."
Five cases have been reported in Maryland in the past eight years, said Dr. Diane M. Dwyer, state epidemiologist. Nationally, an average of about 60 cases a year were confirmed by the Centers for Disease Control and Prevention before 1995, when leptospirosis was dropped as a nationally reportable illness.
Leptospirosis typically causes aches, pains and fever that go away on their own. But one in 10 cases includes high fever, jaundice, meningitis (inflammation of the brain lining), acute kidney failure, internal bleeding and, occasionally, death. It is treatable with antibiotics.
Much as typhoid fever was a marker for poor sanitation in the 1920s, leptospirosis is "a marker of our social environment," said Dr. Joseph M. Vinetz, an author of the study. He is a fellow in infectious diseases at Hopkins and a fellow in parasitic diseases at the National Institutes of Health.
Vinetz thinks deteriorating economic conditions in many inner-city neighborhoods are exacerbating health risks.
Another rat-borne illness, caused by a hantavirus identified in Baltimore, is also being studied at Hopkins. Similar viruses in Korea and Finland have been linked to kidney failure in humans.
Dwyer said the Hopkins paper is evidence that "there are people who get exposed and infected who don't come to the attention of a doctor, or not so that they get diagnostic tests."
"I don't think we've got a huge leptospirosis problem," she said, but "clearly one of the things this makes us look at is, 'How good is our surveillance system?' "
Dr. Peter Beilenson, the city health commissioner, said the city might need to broaden its public school health curriculum to include warnings about infection risks. It already tries to teach children how to deprive rats in alleys of the trash they feed on.
