PHILADELPHIA (September 21, 1999) -- Fire ants attack people who disturb their ant mounds, but they will also attack humans indoors. The September 21, 1999, issue of Annals of Internal Medicine carries two case reports of fire ant attacks in two Mississippi nursing homes. Two elderly patients were found covered with ants, with ant trails leading from the floor to their beds. One died five days after the attack, the other 13 months later. Both facilities had been treated by pest control services in the previous days.

Fire ants arrived in the U.S. about 60 years ago and have spread across the Southeastern U.S. and Puerto Rico. They have consumed most of the native black ant population in the Southeast and have recently been spotted in some Western states, says Richard D. deShazo, MD, lead author of the Annals article, director of the division of allergy and immunology and chairman of the department of medicine at the University of Mississippi Medical Center.

Fire ants sting and kill invertebrates as their primary food source but have been known to kill farm animals if other food isn't available. According to deShazo, the medical complications of fire ant stings can range from mild irritation at the sting site to death from a generalized allergic reaction, depending on the number of stings and the physical condition of the victim.

Fire ant stings at the ant mounds or outdoors have caused at least 80 deaths. But, in 1989, the first case of fire ants attacking humans inside a building was reported. Since then, seven more indoor attacks on people in six states have been reported, six of these by deShazo.

In the ten reported indoor attacks, four of the patients did not suffer clinical complications; a five-day old baby, attacked in a crib, went into shock and coma but lived; a developmentally delayed two-year old suffered damage to his cornea when fire ants attacked his eyes; two older nursing home patients died within six days of attack.

Therefore, in the Southeast and other areas where fire ants are known to live, "any sighting of a swarm of ants indoors is a warning. Residents and caregivers of infants, children and bedridden people, such as patients in health care facilities, should be closely watched until the ants are eliminated," deShazo says. Eliminating fire ants is not easy, says deShazo. The colony cannot be destroyed unless the queen ant is killed. Ants observed in the house, like the ones swarming at an outdoor ant mound, are worker ants, not the queen. To exterminate fire ants, deShazo advises:

Assume that if one fire ant is seen, an active infestation is present. Investigate both interior and exterior of the building carefully. Exterminate all ants found indoors with liquid pesticides as soon as possible. Treat ant activity on the perimeter or basement and in the yard with bait-based insecticides, which are most likely to reach and kill the queen ant. Since fire ants are attracted to electrical fields, examine equipment with wires, fuses and switches. Fire ants may invade electrical equipment, including computers, air conditioners and circuit breakers. DeShazo says that extermination indoors should probably be done by a professional pest control service and that reinfestation is common.

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The American College of Physicians-American Society of Internal Medicine (ACP-ASIM), composed of more than 115,000 internal medicine physicians and medical students, is a non-profit organization dedicated to providing continuing education to its members so that internists may provide the best quality care for their patients. ACP-ASIM is the nation's largest specialty organization and the second largest medical organization.