They're largely invisible, these disease detectives, working without the recognition of their scientific peers who win prizes and publish articles in prestigious journals. And yet they often are the first line of defense to prevent the spread of disease lurking in food, water, air or blood.
While their searches often start with hunches, their training teaches them not to rely too much on this. Suspicions are to be tested through statistics, fieldwork and investigation.
Their task is to solve mysteries in which the answers often are uncertain. These sleuths often are left with a best guess about what befell a group of adults or children, at home at work or out on the town.
Here are three of their cases: *
Hepatitis B is a blood-borne liver disease commonly spread through sex or drug abuse. So how did three women in their 80s, all suffering from dementia and living in the same nursing home, contract the disease late in the summer of 1999, with two of them dying?
Fearing an epidemic, Los Angeles County health officials assigned Dr. Elizabeth Bancroft, a member of an elite corps of federal public health sleuths, to solve that puzzle.
Bancroft, 35, worked for the Epidemic Intelligence Service, part of the federal Centers for Disease Control and Prevention. A native of New York City, she has had a lifelong interest in public health. But fate played a big role in her becoming a disease detective.
After completing medical school and gaining a master's degree in clinical epidemiology from Harvard, she traveled to Indonesia on a prestigious Henry Luce scholarship. A few weeks after her arrival, she was hiking near a dormant volcano when she accidentally plunged down a 40-foot cliff.
Her rescue was delayed because villagers feared going near the volcano, which produced deadly gases. When it began to rain, the villagers--believing rain would diminish the vapors--fashioned a gurney from sarongs and tree branches and carried Bancroft out.
Despite a broken back, skull and ribs, Bancroft, hours from medical help, remained conscious.
"When I fell, I knew instantly what happened," she recalled. She looked at her hiking partner and said: "I can't move my legs. But don't worry, I'll just go back to Harvard and get a PhD in epidemiology."
Damage to her spinal cord left her unable to walk, even after rehabilitation. She opted against getting the doctorate and decided instead to complete her residency in preventive medicine at Cornell University Medical College.
Her first job after leaving Cornell was with the CDC, which assigned her to Los Angeles County's Acute Communicable Disease Control Unit, where she ran across the cases of hepatitis B at the nursing home.
While trying to determine the source of the three women's infections, she also needed to know how many other people might have been exposed to hepatitis B, which is highly infectious in minuscule doses.
What did they have in common?
Complicating her investigation, the nursing home had closed and its residents were scattered among 18 other facilities.
Bancroft led a team of health department investigators who painstakingly tracked down each former resident and requested blood tests to look for hepatitis B infections.
Of the 38 surviving residents they found, five showed evidence that they'd been infected in the past, although they weren't sick at the time of the tests. Of the remaining 33, the only risk factors the investigators could associate with the illness were their being diabetic and having their blood sugar tested with skin-pricking devices.
Then a fourth hepatitis case was discovered: a 78-year-old man with no outward symptoms of the disease.
Because the man was an amputee in a wheelchair, it appeared unlikely he would be the source of infection for the three women, so that helped Bancroft rule out sexual abuse, she said. At this point, she began following up her suspicion that the hepatitis B infections had something to do with being diabetic.
Bancroft then turned to an important part of any epidemiologic investigation.
She began digging into medical literature, finding other reports about finger-stick devices spreading hepatitis B.
She soon quizzed nurses from the old nursing home about blood-testing. They had used pen-like, spring-loaded devices. Although they inserted a new lancet for each patient, they reused the pen after wiping off its case and cap with alcohol.
"They thought they were doing the right thing," Bancroft said.
Problem was, alcohol wasn't touching tiny micro-droplets of blood trapped behind the cap. As the device forced a new lancet into the next patient's finger, it probably carried infectious blood with it.
Although it's impossible to be 100% certain, Bancroft said the four cases most likely resulted from reusing the devices.
Bancroft's Epidemic Intelligence Service assignment ended last week. However, she is staying on with the county to investigate hospital-based infections and blood-borne diseases.
"The reason I wanted to come here," she says, "is that Los Angeles has great bugs."