Covert chemical attack may be hard to detect

CDC warning includes signs of symptoms

Media images to the contrary, a chemical terrorist attack may not be so obvious as people choking in a subway or being hosed down and decontaminated in the streets.

On the contrary, a chemical attack actually could go undetected until an alert epidemiologist begins putting the pieces together, warns the Centers for Disease Control and Prevention (CDC).

"Most people, when they think of chemicals, they focus on what happened in Tokyo with the sarin gas being released in the subway, or things like a tanker truck full of chemicals being exploded," says Martin Belson, MD, medical toxicologist with the CDC national center for environmental health.

"We want to make sure they are also focused on deliberate poisoning of various media like food or water. It may be a little more insidious, where depending on the distribution of that food and water, they may kind of trickle into different EDs or to their doctor. It may not be an overwhelming mass of people becoming ill," he points out.

To help health care workers recognize a chemical release-related illness, the CDC recently identified examples of chemical-induced illness.1 (See table.)

A covert release of a chemical agent might not be identified easily for at least five reasons:

1. Symptoms of exposure to some chemical agents (e.g., ricin) might be similar to those of common diseases (e.g., gastroenteritis).

2. Immediate symptoms of certain chemical exposures might be nonexistent or mild despite the risk for long-term effects (e.g., neurocognitive impairment from dimethyl mercury, teratogenicity from isotretinoin, or cancer from aflatoxin).

3. Exposure to contaminated food, water, or consumer products might result in reports of illness to health care providers over a long period and in various locations.

4. People exposed to two or more agents might have symptoms not suggestive of any one chemical agent (i.e., a mixed clinical presentation).

5. Health care providers might be less familiar with clinical presentations suggesting exposure to chemical agents than they are with illnesses that are treated frequently.

Vital clues may tell tale

Epidemiologic clues that might suggest the covert release of a chemical agent include:

  • an unusual increase in the number of patients seeking care for potential chemical release-related illness;
  • unexplained deaths among young or healthy people;
  • emission of unexplained odors by patients;
  • clusters of illness in people who have common characteristics, such as drinking water from the same source;
  • rapid onset of symptoms after an exposure to a potentially contaminated medium (e.g., paresthesias and vomiting within minutes of eating a meal); unexplained death of plants, fish, or animals (domestic or wild);
  • a syndrome (i.e., a constellation of clinical signs and symptoms in patients) suggesting a disease commonly associated with a known chemical exposure (e.g., neurologic signs or pinpoint pupils in eyes of patients with a gastroenteritis-like syndrome or acidosis in patients with altered mental status).


1. Centers for Disease Control and Prevention. Recognition of illness associated with exposure to chemical agents. MMWR 2003; 52(39): 938-940.