More than 3,700 patients stricken with nausea, vomiting, and diarrhea have visited Boston's emergency rooms during the past six weeks in a wave of gastrointestinal illness that has swept cities across North America.
Federal health authorities are so concerned that they will conduct a telephone conference call this week with disease trackers from across the nation to gauge the impact of an outbreak attributed to norovirus, an intestinal germ that travels easily from person to person. Dr. Marc-Alain Widdowson, a norovirus specialist at the US Centers for Disease Control and Prevention , said the current outbreak of illness appears to be the worst since 2002-2003.
"But the bottom line is we don't really know why," said Widdowson, who speculated that the virus currently circulating may be a different strain, one that is more easily transmitted or one that spawns more severe symptoms.
For Dr. Anita Barry , Boston's director of communicable disease control, any lingering doubts about the breadth and severity of the outbreak were erased when she saw figures delineating ER visits on Christmas -- a day when patients do almost anything to avoid a trip to the hospital. On that day, 73 patients with gastrointestinal woes turned up in Boston's 10 emergency rooms.
"If people are coming to the emergency room on Christmas Day," Barry said, "that suggests to me this illness is more severe than your routine gastrointestinal illness."
Day by day, the Boston Public Health Commission has been tracking the march of the intestinal infection, using a surveillance network that monitors patients' ailments in emergency rooms. It creates something akin to a daily Dow Jones of disease, showing trends in infectious illnesses and other medical conditions.
The network, activated shortly before the Democratic National Convention in 2004, acts as an early-warning system that gives health authorities a potentially decisive edge in their battle with microscopic foes.
The system does not provide an actual diagnosis, but it can identify clusters of patients with similar symptoms.
"This gives us a clue earlier on that something may be up," Barry said.
By the middle of December, Barry knew that the increase in ER patients with their hands clutching their stomachs was no fluke. And while the volume fluctuated, it was generally increasing.
Health Commission specialists know more than just how many people are coming to the ER: They also know patients' ages and their ZIP codes. While certain neighborhoods were hit harder than others -- Roxbury had the highest concentration of gastrointestinal illness -- no community escaped the virus.
That was another major clue for disease specialists, and it showed them that they needed to direct their efforts to the whole city, not just individual communities. City health authorities said they do not know for sure why certain neighborhoods generated more ER visits, but speculated it could reflect everything from patients lacking primary care physicians to some neighborhoods having greater population density, allowing the virus to spread more swiftly.
Sophisticated, real-time disease-tracking systems had been in the works for years, but the terrorist attacks of Sept. 11, 2001, as well as the arrival of anthrax-laden letters a month later, caused researchers to expedite development of the networks. Initially, the tracking systems, known as syndromic surveillance networks, were trumpeted for their potential to detect bioterror attacks.
But since dozens of public and private health agencies activated the networks, specialists have increasingly recognized that the first-generation systems now in operation may be better suited for identifying large outbreaks of gastrointestinal and respiratory illnesses.
"Diseases that tend to have explosive onset with a large number of cases early on do show up quite nicely," said Dr. James Nordin , a clinical investigator at HealthPartners Research Foundation in Minnesota, which runs a tracking system in the Twin Cities.
Norovirus is one of those diseases. And the consequences are seen in hospitals like Boston Medical Center , where ER doctors have treated a steady stream of patients.
"We have seen a large number of cases of what appears to be a sudden onset and intense, short-lived diarrhea, nausea, and some abdominal pain," said Dr. Jonathan Olshaker , Boston Medical's emergency department chief. "Although if you're going through it, it doesn't seem short-lived."
Stephen Smith can be reached at email@example.com.