Skip Navigation LinksSkip Navigation Links
Centers for Disease Control and Prevention
Safer Healthier People
Blue White
Blue White
bottom curve
CDC Home Search Health Topics A-Z spacer spacer
Blue curve MMWR spacer

Bioterrorism Alleging Use of Anthrax and Interim Guidelines for Management -- United States, 1998

From October 30 through December 23, 1998, CDC received reports of a series of bioterroristic threats of anthrax * exposure. Letters alleged to contain anthrax were sent to health clinics on October 30, 1998, in Indiana, Kentucky, and Tennessee. During December 17-23 in California, a letter alleged to contain anthrax was sent to a private business, and three telephone threats of anthrax contamination of ventilation systems were made to private and public buildings. All threats were hoaxes and are under investigation by the Federal Bureau of Investigation (FBI) and local law enforcement officials. The public health implications of these threats were investigated to assist in developing national public health guidelines for responding to bioterrorism. This report summarizes the findings of these investigations and provides interim guidance for public health authorities on bioterrorism related to anthrax.


The threatening letter was opened by an administrative assistant, who called 911; police, fire, emergency medical services (EMS), and hazardous materials units (HAZMAT) (i.e., first responders) were sent to the clinic, and the local FBI office was contacted. The letter was sealed in a plastic bag and collected by FBI. All 31 adults who were in the building when the letter was opened were considered possibly exposed to Bacillus anthracis spores and were detained for approximately 3 hours.

First responders in consultation with public health officials in the Marion County Health Department (MCHD) decontaminated the potentially exposed persons in a temporary shelter constructed on the scene. HAZMAT personnel used full protective gear with self-contained respirators (level A protection). The 31 occupants placed their clothing and personal effects in plastic bags and showered using soap and water plus a dilute bleach solution. The desktop where the letter was opened was washed with a 5% hypochlorite solution (i.e., standard household bleach). All 31 persons were transported to local emergency departments (EDs) to receive oral chemoprophylaxis with ciprofloxacin (500 mg twice daily); some underwent additional decontamination (i.e., showered again with soap and water) as required by hospital policy.

Public health officials from the MCHD collected contact information from all persons and informed them they would be notified when results from laboratory testing were available; arrangements also were made for counseling. The letter was taken by FBI to the Indiana State Department of Health Laboratory, where cultures for B. anthracis were negative. The next day, FBI transported the letter to the United States Army Medical Research Institute for Infectious Diseases (USAMRIID), U.S. Department of Defense, in Ft. Detrick, Maryland, where direct fluorescent antibody testing and culture were negative.


The letter was opened by an administrative assistant; the assistant called the postal inspector and was advised to put the letter in a plastic bag. The postal inspector contacted the local FBI office and went to the clinic. FBI contacted the assistant fire chief who sent police, fire, EMS, and a HAZMAT unit to the clinic.

Jefferson County Health Department personnel recommended that the staff member and the postal inspector shower with soap and water at the clinic and obtain oral chemoprophylaxis (ciprofloxacin 500 mg twice daily) at a local ED. The Kentucky State Department for Public Health, FBI's Weapons of Mass Destruction Office, and USAMRIID advised that decontamination and oral chemoprophylaxis were not necessary for five other adults in the center who may have been exposed to the letter. The desktop where the envelope had been opened was decontaminated with a hypochlorite solution.

The letter was taken by FBI to a biosafety level 3 facility at the University of Louisville Hospital Clinical Microbiology Laboratory, where phase microscopy revealed no spores consistent with B. anthracis, and cultures were negative. The next day, FBI transported the letter to USAMRIID, where direct fluorescent antibody testing and culture were negative.


The letter was opened by an administrative assistant, who called the local police department; officers took custody of the letter and placed it in a plastic bag. A clinic administrator contacted CDC seeking advice about preventive health measures. CDC notified the local FBI field office and the Tennessee Department of Health regarding the threat. FBI took the letter from the local police department to USAMRIID, where tests were negative for B. anthracis. The administrative assistant and the responding police officer, both of whom had direct contact with the letter, received chemoprophylaxis.


During December 17-23, 1998, four threats alleging use of anthrax were reported in greater metropolitan Los Angeles. The response to all four threats involved the police and fire departments, EMS, HAZMAT, FBI, the County of Los Angeles Department of Health Services (CLADHS), the California Department of Health Services, and CDC.

The first threat was a letter mailed to a private business; all 28 adults considered at risk for exposure to B. anthracis were decontaminated at the scene and given chemoprophylaxis. The letter was transported by FBI to a CLADHS biosafety level 3 laboratory and cultured for B. anthracis; all cultures were negative.

In the second threat, a telephone caller to a government building claimed to have contaminated the building's air-handling system. Approximately 95 adults received chemoprophylaxis. First responders, FBI, and CLADHS jointly decided not to decontaminate involved persons.

In the third threat, a telephone caller to 911 claimed to have contaminated the air-handling system of a federal building with B. anthracis; 1200-1500 persons (at least one of whom was pregnant) and two children potentially were exposed. Contact information for potentially exposed persons was collected for follow-up. No one was decontaminated on the scene, and chemoprophylaxis was not recommended; all potentially exposed persons were asked to go home, wipe down the interiors of their potentially contaminated vehicles with a solution of one part bleach to 10 parts water, place their clothing in a plastic bag until results from laboratory testing were known, and then shower. Environmental samples taken from the air ducts of the building were cultured for B. anthracis at CLADHS; all cultures were negative.

In the fourth incident, an anonymous telephone caller to 911 claimed to have contaminated the air-handling system of an office building occupied by approximately 200 persons. FBI was contacted; the threat was deemed to have low credibility. FBI in conjunction with CLADHS decided that neither decontamination nor chemoprophylaxis was warranted. Environmental samples tested at CLADHS were negative for B. anthracis.

Reported by: Marion County Health Dept, Indianapolis; Indiana State Dept of Health. Jefferson County Health Dept, Louisville; Kentucky Dept for Public Health. Knox County Health Dept, Knoxville; Tennessee Dept of Health. County of Los Angeles Dept of Health Svcs, Los Angeles; California Dept of Health Svcs. Council of State and Territorial Epidemiologists, Atlanta, Georgia. Federal Bur of Investigation, Washington, DC. US Army Medical Research Institute for Infectious Diseases, US Dept of Defense, Ft. Detrick, Maryland. Office of Emergency Preparedness, US Dept of Health and Human Svcs. Emergency Response Coordinating Group, National Center for Environmental Health; Meningitis and Special Pathogens Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; and an EIS Officer, CDC.

Editorial Note

Editorial Note: Anthrax is an acute infectious disease caused by the spore-forming bacterium B. anthracis. It occurs most frequently as an epizootic or enzootic disease of herbivores (e.g., cattle, goats, and sheep), which acquire spores from direct contact with contaminated soil. Humans usually become infected through contact with or ingestion or inhalation of B. anthracis spores from infected animals or their products (e.g., goat hair). Human-to-human transmission has not been documented.

Although all the threats alleging use of anthrax described in this report were hoaxes, they demonstrate settings where bioterrorism can occur and the potential public health impact. These threats required prompt action by health, law enforcement, and laboratory personnel. Coordination and communication across agencies are necessary to protect the public and first responders from credible biologic warfare and bioterrorism agents such as anthrax.

The spore form of B. anthracis is durable and can be delivered as an aerosol (1). The incubation period for anthrax is 2-60 days. Inhalation causes the most serious form of human anthrax, and although contemporary experience in humans is limited, mortality may be high even with appropriate therapy (T.V. Inglesby, D.A. Henderson, J.G. Bartlett, et al., Working Group for Civilian Biodefense, personal communication, 1998). The likelihood of developing cutaneous disease is low after exposure of B. anthracis spores to intact skin. The risk for "secondary" anthrax through reaerosolization appears to be low in settings where B. anthracis spores were released unintentionally or were present at low levels (2). In situations where the threat for transmission of B. anthracis spores is deemed credible, decontamination of skin and potential fomites (e.g., clothing or desks) may be considered to reduce the risk for cutaneous and gastrointestinal forms of disease.

Planning for Response to Threats

The public health response to bioterrorism requires communication and coordination with first responders and law enforcement officials. State and local health departments should work with these groups to ensure that local disaster preparedness plans address bioterrorism; define the roles of each agency, including protection of first responders; and are tested through simulations. FBI has jurisdiction for bioterrorism response but recognizes the need to conduct epidemiologic investigations, define at-risk groups, and rapidly implement potentially life-saving medical and public health responses. When bioterrorism alleging use of anthrax or other agents occur, the local emergency response system should be activated by dialing 911 in most communities; in communities without 911 systems, local law enforcement authorities should be notified. The local FBI field office and local and state public health authorities also should be notified.

FBI will coordinate the collection of evidence (e.g., letters, packages, or air-handling system samples) and deliver materials to an FBI or U.S. Department of Defense laboratory for testing. To guide decision-making, test results identifying B. anthracis should be available as soon as possible, at least within 24-48 hours. Efforts are under way to assess and enhance the capabilities of state and local health department laboratories to fulfill the need for rapid analysis. Planning for laboratory testing should be part of bioterrorism preparedness by state and local public health, law enforcement, and first responder authorities in consultation with federal officials.

Public health officials, working with law enforcement and first response personnel, should determine the need for decontamination and postexposure prophylaxis. In most of the recent hoaxes purporting anthrax exposure, immediate postexposure decontamination and prophylaxis have not been indicated because of the lack of credibility of the threat. Public health officials should collect contact information for potentially exposed persons for notification of laboratory results or other follow-up. Potentially exposed persons should be given information about the signs and symptoms of illnesses associated with the biologic agent and about whom to contact and where to go should they develop illness.

Recommendations for Postexposure Prophylaxis

Postexposure prophylaxis for exposure to B. anthracis consists of chemoprophylaxis and vaccination. Oral fluoroquinolones are the drugs of choice for adults, including pregnant women (T.V. Inglesby, D.A. Henderson, J.G. Bartlett, et al., Working Group for Civilian Biodefense, personal communication, 1998; 3) (Table_1). If fluoroquinolones are not available or are contraindicated, doxycycline is acceptable. Children should receive prophylaxis with oral ciprofloxacin or oral doxycycline (T.V. Inglesby, D.A. Henderson, J.G. Bartlett, et al., Working Group for Civilian Biodefense, personal communication, 1998; 3) (Table_1). Prophylaxis should continue until B. anthracis exposure has been excluded.

Postexposure vaccination with an inactivated, cell-free anthrax vaccine (Bioport Corporation, formerly Michigan Biologic Products Institute **) is indicated in conjunction with chemoprophylaxis following a proven biologic incident (T.V. Inglesby, D.A. Henderson, J.G. Bartlett, et al., Working Group for Civilian Biodefense, personal communication, 1998; 4). Postexposure vaccination consists of three injections: as soon as possible after exposure and at 2 and 4 weeks after exposure. Anthrax vaccine can be requested through CDC. Although this vaccine is now being administered routinely to U.S. military personnel, routine vaccination of civilian populations is not recommended. This vaccine has not been evaluated for safety and efficacy in children aged less than 18 years or adults aged greater than 60 years.

If decontamination is appropriate, persons should remove their clothing and personal effects, place all items in plastic bags, and shower using copious quantities of soap and water (5). Plastic bags with personal effects should be labeled clearly with the owner's name, contact telephone number, and inventory of the bag's contents. Personal items may be kept as evidence in a criminal trial or returned to the owner if the threat is unsubstantiated. For incidents involving possibly contaminated letters, the environment in direct contact with the letter or its contents should be decontaminated with a 0.5% hypochlorite solution (i.e., one part household bleach to 10 parts water) following a crime scene investigation. Personal effects may be decontaminated similarly.

CDC and other offices in the U.S. Department of Health and Human Services are working with state and local health departments, federal agencies, and nongovernmental organizations to improve the public health capacity to address bioterrorism and develop locality-specific response plans. CDC also can assist public health officials with decision-making if a threat occurs alleging the use of a biologic agent.


  1. Pile JC, Malone JD, Eitzen EN, Friedlander AM. Anthrax as a potential biological warfare agent. Arch Intern Med 1998;158:429-34.

  2. Meselson M, Guillemin J, Hugh-Jones M, et al. The Sverdlovsk anthrax outbreak of 1979. Science 1994;266:1202-8.

  3. Franz DR, Jahrling PB, Friedlander AM, et al. Clinical recognition and management of patients exposed to biological warfare agents. JAMA 1997;278:399-411.

  4. Friedlander AM, Welkos SL, Pitt MLM, et al. Postexposure prophylaxis against experimental inhalation anthrax. J Infect Dis 1993;167:1239-43.

  5. U.S. Army Medical Research Institute for Infectious diseases/CDC/Food and Drug Administration. Medical response to biological warfare and terrorism {Satellite broadcast}. Atlanta, Georgia: US Department of Defense/US Department of Health and Human Services, CDC, September 22-24,1998.

Infection caused by the bacterium Bacillus anthracis. ** Use of trade names and commercial sources is for identification only and does not imply endorsement by CDC or the U.S. Department of Health and Human Services.

Note: To print large tables and graphs users may have to change their printer settings to landscape and use a small font size.

TABLE 1. Recommended postexposure prophylaxis for exposure to Bacillus anthracis*
Drug                       Adults                Children+
Oral fluroquinolones
  One of the following:
    Ciprofloxacin          500 mg twice daily    20-30 mg per kg of body mass
                                                   per day divided every 12
    Levofloxacin           500 mg once daily     Not recommended
    Ofloxacin              400 mg twice daily    Not recommended

If fluoroquinolones
   are not available
   or are contraindicated
    Doxycycline            100 mg twice daily    5 mg per kg of body mass per
                                                   day divided every 12 hours
*  Prophylaxis should continue until exposure to B. anthracis has been excluded. If exposure
   is confirmed, prophylaxis should continue for 4 weeks and until three doses of vaccine have
   been administered or for 8 weeks if vaccine is not available.
+  Use of tetracyclines and fluoroquinolones in children has well-known adverse effects; these
   risks must be weighed carefully against the risk for developing life-threatening disease. If a
   release of B. anthracis is confirmed, children should receive oral amoxicillin 40 mg per kg of
   body mass per day divided every 8 hours (not to exceed 500 mg three times daily) as soon
   as penicillin susceptibility of the organism has been confirmed.

Return to top.

Disclaimer   All MMWR HTML versions of articles are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the electronic PDF version and/or the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to

Page converted: 02/04/99


Safer, Healthier People

Morbidity and Mortality Weekly Report
Centers for Disease Control and Prevention
1600 Clifton Rd, MailStop E-90, Atlanta, GA 30333, U.S.A


Department of Health
and Human Services

This page last reviewed 5/2/01