The findings of this study extend the data on adherence with postexposure prophylaxis and substantiate other similar surveys (11)
. Despite concerns about the safety of postal workers with potential exposures to B. anthracis
, our survey demonstrates that many workers did not take adequate prophylaxis. Adherence in this population was apparently affected by a low perceived risk for anthrax and a concern about side effects. Concern about side effects was present even before postal workers started taking antibiotics; 47% of the 32 workers who never started prophylaxis cited concern about side effects as a reason. Although many workers did experience side effects, the side effects they reported were not severe. In addition, many postal workers had difficulty taking their medications as prescribed, and they missed doses of prophylaxis.
Two factors may have contributed to the low perceived risk of inhalational anthrax among postal workers. First, results from the first three efforts to collect samples at the postal facilities and the nasal swabs taken at the onset of the investigation were negative for anthrax spores. Second, postal, medical, and union leaders providing information on environmental sampling results and their interpretation at USPS town meetings tried to put the risk in the perspective as explained to them by the Department of Public Health. Overall, the data suggested a possible, but not high, risk for inhalational anthrax. Spores were likely introduced in mid-October before the New Jersey and Washington D.C. regional distribution centers that handled the contaminated Daschle and Leahy letters closed down. Use of compressed air to clean sorting machines, which might have caused aerosolization of spores, had ceased by October 23, when a general USPS advisory against it was circulated. Maximum risk of exposure to aerosolized spores likely occurred during that time. By the time the postexposure prophylaxis clinics began, 30–40 days had passed since the maximum risk period without the occurrence of any cases of inhalational anthrax in regional facility workers. In addition, the initial samples taken on November 11 and 21, with methods that readily identified spores in New Jersey and Washington, D.C., had failed to identify any spores. These factors were discussed during town meetings in an effort to reassure postal workers, while still emphasizing that a period did occur when spores were in the air, especially around the sorting machines.
In this setting, the numbers of postal workers who accepted antibiotics could not be used as a measure for the numbers of postal workers who actually took prophylaxis. Anecdotally, many postal workers reported obtaining the antibiotics to “have on hand” in the event “I start to feel sick.” The postexposure prophylaxis survey was critical in determining the level of adherence and identifying issues affecting adherence in this population.
The circumstances of this prophylaxis campaign, along with the small sample size and potential for recall bias associated with this survey, limit the inferences that may be drawn. For example, some misclassification of side effects as doxycycline- or ciprofloxacin-related may have accompanied the switch in medications. In addition, the study size limits any speculation as to the nature of the relationship between being men and starting prophylaxis. Larger postexposure prophylaxis surveys may identify the reason for this and other associations that were not significant in our analysis. Nonetheless, the survey provided important information on adherence to prophylaxis and reasons for nonadherence.
In the event of another bioterrorism attack, public health officials must communicate, early and effectively, the need for potentially exposed persons to initiate and continue postexposure prophylaxis. Specifically, officials should clearly communicate to at-risk persons the explanation that epidemiologic tools such as nasal swabs are poor indicators of past personal exposure and are, at best, indicators only of recent exposure. While important, reassurance must be balanced with clear explanations of risk. Of note in our study is the fact that the one group deemed to be at higher risk—those working on high-speed mail sorting machines—was found no more likely to begin or continue on prophylaxis than persons working elsewhere in the facility.
Potentially exposed persons need to be aware that side effects are to be expected, but that the vast majority of side effects will be mild. Education should center on how to recognize and minimize minor side effects while describing which side effects require immediate medical assistance. Amelioration of side effects is essential if persons are to stay on their regimens, especially if the time period is lengthy. In addition, antibiotic reminder programs such as signs in common areas or buddy systems may improve adherence to postexposure prophylaxis.
In conclusion, if public health officials deem initiating prophylaxis programs necessary, conducting frequent follow-up surveys to measure adherence and identify obstacles to prophylaxis in a specific population will be important in identifying perception problems and maximizing the benefits of preventive therapy.