By Emma Hitt, PhD

ATLANTA (Reuters Health) – Confirming the experience of more than 1000 Florida media company employees treated last month, many postal workers using antimicrobial prophylaxis for anthrax are reporting adverse reactions.

Overall, 19% of the respondents taking ciprofloxacin have reported severe nausea, vomiting, diarrhea, or abdominal pain; 14% have reported fainting, light-headedness, or dizziness; 7% have reported heartburn or acid reflux; and 6% have reported rashes, hives, or itchy skin, researchers from the US Centers for Disease Control and Prevention note in the November 30th issue of Morbidity and Mortality Weekly Report.

As Reuters Health reported on November 8, adverse events were reported by about 20% of the 1132 people at American Media Inc. in Boca Raton, Florida who received antimicrobial prophylaxis after the first recent US case of inhalation anthrax was documented there.

In the latest investigation, a questionnaire evaluating the occurrence of adverse events was administered to postal employees in New Jersey, New York City, and the District of Columbia 7 to 10 days after they were offered antimicrobial prophylaxis. A total of 5819 postal workers responded to the questionnaire, and of those, 3863 (66%) reported that they had initiated prophylaxis.

Of those who had initiated prophylaxis, 89% reported using ciprofloxacin and 11% used other antimicrobials (when ciprofloxacin was contraindicated), including doxycycline (6%) and amoxicillin (1%).

The rates of adverse events were higher in NJ compared with NYC and DC, a finding that the CDC suggests may be explained by the different mode of administration of the questionnaires (nurses in NJ versus self-administered in NYC and DC).

Overall, 8% of those taking ciprofloxacin reported discontinuing the medication because of adverse events or fear of adverse events, or because they thought they did not need it.

A total of 82 people (2%) sought medical attention for symptoms that may have been associated with anaphylaxis. The CDC researchers note that "among the 33 persons who sought medical attention for these symptoms in NJ and NYC, none was hospitalized and none of the symptoms was attributed to antimicrobial prophylaxis by clinicians who evaluated these persons."

The CDC stresses that "among persons with exposures to B. anthracis related to the recent bioterrorist attacks, completion of a full 60-day course of antimicrobial prophylaxis is essential for preventing anthrax."

According to Dr. Nancy Rosenstein, a medical officer with the CDC's National Center for Infectious Diseases, people who have adverse reactions to their antibiotics and are at risk for anthrax should be switched to another antibiotic if appropriate and should be counseled about taking antibiotics.

During a telephone press conference on Thursday, she emphasized that the data being reported are only for the 10 days after the start of prophylaxis. "We are going to continue to monitor people for side effects throughout the course of their antibiotics, and there will be more data on that in the next couple of months," she said.

MMWR 2001;50:1031-1034.