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: *
Of the 70 guests who helped a San Fernando Valley boy celebrate his 16th birthday early last month, 28 began developing high fevers, vomiting and diarrhea a day later.
Because the symptoms indicated a more serious illness than routine food poisoning, Dr. Douglas Frye and his Los Angeles County health department colleagues began searching for an explanation a few days later.
Fortunately, no one had died or been hospitalized. But there was concern this might represent part of a larger outbreak.
Frye and his team suspected they might have been dealing with salmonella, shigella or campylobacter--three common food-borne bacterial infections.
The investigators worked the phones to determine who got sick and when, what and how much they ate, where it came from and how it became contaminated. Nothing is simple.
The hostess of the June 3 party served sandwiches delivered by a local deli; snacks from a supermarket and a superstore; chocolate cake from a caterer; watermelon sliced at home; strawberries picked in Moorpark; coleslaw and onion dip she'd prepared herself.
County officials tracked down every guest to determine whether any of them worked in jobs such as health care or food service where they might inadvertently spread the illness.
Food inspectors visited the deli that delivered the 6-foot sandwiches. There, they found improperly chilled meats and cheeses that were immediately set aside. The health department later ordered them discarded.
The hostess turned over leftovers for tests.
Lab tests were done on stool samples from guests who had become ill.
"It's really early, and yet it's really late already," said Frye, explaining that some guests had taken antibiotics that killed off the evidence of what sickened them.
Because the kids developed diarrhea and fever, the team first considered common bugs.
At this point, four days after the party, listeria monocytogenes--a bug potentially fatal to the elderly, infants or anyone who has a weak immune system--wasn't likely. Listeria infections, responsible for 2,500 flu-like illnesses and 500 deaths each year, usually don't develop until a month after exposure, when they can produce blood infections and meningitis in infants, the elderly and people with weak immune systems. But Frye was dealing with young, healthy teens who became very sick in days; only fairly high doses of listeria would give them the high fevers, diarrhea and vomiting they developed.
The incubation period--the time between exposure and symptoms --is key to disease detection, he said. But, he added, "it can burn you too."
Frye had done this many times. A specialist in preventive medicine, he's been an epidemiologist with the county for nine months after spending two years with the CDC's Epidemic Intelligence Service. He's been a youth advisor and a hospice volunteer, and he spent years tending to the health needs of the homeless in San Francisco.
He is witty and curious, with patience to explain and energy to burn. Asked about his own caution with food, he admitted to taking chances with sushi but shunning Caesar salads with raw-egg dressings.
On June 15, Frye called to say laboratory tests confirmed that listeria was the culprit. It fooled everyone for a while, but that's why the lab work was so crucial.
Laboratory cultures identified listeria in the stools of three sickened guests and on the leftover turkey and Jack cheese sandwiches from the deli.
Once again, it was back to the phones to warn party-goers that if they developed symptoms, they should see a doctor and discuss their potential exposure to listeria. The disease detectives continued hunting for anyone who ate food in the previous three weeks catered by the same deli.
So far, there are no new cases.