March 26, 2012

Public health 'detectives' tracked clues to illness' cause

By Meredith Goad
Staff Writer

Second of two parts

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Cathy Dragoni, who manages the microbiology department at NorDx, holds control examples of salmonella cultures at the Scarborough laboratories late last month. NorDx offers a variety of testing services for salmonella and other pathogens.

John Ewing/Staff Photographer

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Dr. Stephen Sears, state epidemiologist: "Some people think there’s a case of salmonella today and we know about it tomorrow, and it doesn’t work that way.”

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The USDA has failed to require retailers to track what goes into hamburger meat -- even though better records would protect consumers from some food-borne illnesses.

Most retailers, including Hannaford, do not keep those detailed records and have chosen not to follow federal recommendations to do so.

Federal officials and food safety experts do not believe the salmonella contamination in last year's outbreak happened at Hannaford.

The USDA never found the source of contamination.

During the first two weeks of October, a Cumberland County resident ingested something nasty -- a virulent bug known as salmonella that thrives in uncooked ground beef.

The bacteria went on the attack, and sometime over the next three days this person started experiencing painful and distressing symptoms that likely included violent diarrhea, abdominal cramps and fever.

A doctor did an examination and sent a stool sample to a local laboratory. On Oct. 22, that sample tested positive for salmonella. The laboratory worker who did the test, required by law to report cases of salmonella, immediately notified the Maine Health and Environmental Testing Laboratory in Augusta.

Over the next few weeks, three more Mainers were stopped in their tracks by a similar sudden illness. And more incidents were being reported in Massachusetts, New York, New Hampshire, Vermont, Kentucky and Hawaii.

So began two months of medical sleuthing during which public health investigators in seven states quizzed people who got sick about their eating habits and other personal routines, trying to piece together the puzzle.

Ultimately, this detective work, along with technology that helped link together the 20 known cases, led investigators to the source of the illness -- ground beef sold at Hannaford supermarkets.

This type of public health investigation is a long process that unfolds in its own time, controlled by the nature of the disease, the timing of laboratory tests and old-fashioned legwork.

"Some people think there's a case of salmonella today and we know about it tomorrow, and it doesn't work that way," said Dr. Stephen Sears, Maine's state epidemiologist.

There are 40,000 cases of salmonella reported in the United States every year, according to the federal Centers for Disease Control and Prevention, making it the most common cause of foodborne illness. Add in cases that go undiagnosed or unreported, and the actual number of infections may be as much as 1.2 million.

The total number of foodborne illnesses is even higher. The CDC estimates that 1 in 6 Americans, or 48 million people, are sickened by a foodborne pathogen each year.

In the state's public health lab, the microbe ingested by that first Cumberland County patient was identified as Salmonella Typhimurium -- a rarer strain of salmonella that is resistant to antibiotics, and therefore may be more likely to lead to hospitalization.

"All salmonellas are related to each other, but just like people have some genetic distinguishing factors, there are some genetically distinguishing aspects to salmonella," Sears explained. "And that's found through what's called PFGE, which stands for pulsed-field gel electrophoresis. That's a genetic examination of the organism, and so you're looking at the genetic pattern."

The microbe's genetic fingerprint went into a national database called PulseNet so that it could be compared to salmonella samples uploaded by scientists in other parts of the country. This molecular surveillance system helps investigators link cases of foodborne illness even though they may have happened hundreds of miles apart. It greatly speeds up the process of determining whether a case is an isolated incident, or part of a larger outbreak.

As more people became ill in the Hannaford outbreak, a lab worker in Augusta uploaded the Maine salmonella samples into the system. An epidemiologist at the federal CDC in Atlanta who regularly reviews these and other samples sent in from all over the country, searched for matches that would signal an outbreak.

A week after the Cumberland County resident's case was reported to the state, another case came in from Androscoggin County. Two weeks later, there was a third case reported from Waldo County. Then a fourth one came in from York County at the end of November.

(Continued on page 2)

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