Follow-Up of Deaths Among U.S. Postal Service Workers Potentially Exposed to Bacillus anthracis --- District of Columbia, 2001--2002

In October 2001, two letters contaminated with Bacillus anthracis spores were processed by mechanical and manual methods at the U.S. Postal Service (USPS) Brentwood Mail Processing and Distribution Center in the District of Columbia. Four postal workers at the Brentwood facility became ill with what was diagnosed eventually as inhalational anthrax; two died. The facility was closed on October 21, and postexposure prophylaxis was recommended for approximately 2,500 workers and business visitors (1). Subsequent reports of deaths of facility workers prompted concern about whether mortality was unusually high among workers, perhaps related to the anthrax attacks. To evaluate the rates and causes of death among workers at the Brentwood facility during October 12, 2001--October 11, 2002, CDC, in collaboration with state and local health departments, analyzed death certificate data. In addition, these data were compared with aggregate mortality data from the five USPS facilities contaminated with B. anthracis during the fall 2001 anthrax attacks. This report summarizes the results of that analysis, which indicate that rates and causes of death among Brentwood workers during the 12 months after the anthrax attacks of 2001 were not different from rates and causes of deaths that occurred during the preceding 5 years.

Deaths among Brentwood workers were identified through review of death certificates, which were obtained from the USPS Office of Personnel Management, the District of Columbia Health Department, and state health departments in Maryland and Virginia. Cause-specific deaths were compared with actuary/mortality tables from the National Center for Health Statistics. Aggregate mortality data for the five USPS facilities were obtained from the USPS Human Resources Management. Death rates for each USPS fiscal year were calculated by dividing the total number of deaths occurring at the respective facility by the number of USPS personnel assigned to that facility as of October 12, 2001. For each contaminated postal facility, a general linear model was used to compare death rates during the 5 years preceding the study period with the death rate during the study period.

During the study period, 2,646 persons were employed at the Brentwood facility; 2,434 (92%) were black, and 1,496 (57%) were male. A total of 11 deaths occurred among facility workers during this period, excluding the two deaths resulting from known inhalational anthrax (Table 1); deaths occurred during eight of 12 months. Of the 11 deaths, 10 (91%) were among blacks, and four (36%) were among female workers; these proportions were not statistically different from the expected proportion of deaths in this population. The median age of workers at death was 56 years (range: 43--65 years) for both males and females, compared with the median worker age of 52 years (range: 25--75 years). Six (55%) deaths resulted from heart disease, two (18%) from malignant neoplasm, two (18%) from liver disease, and one from septicemia after a prolonged coma resulting from a cerebrovascular accident. On the basis of comparisons with U.S. mortality data (2), the rates of these causes of death among Brentwood workers during the study period did not differ from the rates for expected causes of death for the U.S. population, adjusted for age and race. Although annual death rates for workers from the five contaminated USPS facilities varied, consistent with differences in demographics, no statistically significant differences were observed between death rates during the study period and those during the 5 years preceding the study period (Table 2).

Reported by: K Berry, MD, S Colvin, MD, District of Columbia Health Dept. D Blythe, MD, Maryland State Dept of Health. RB Stroube, MD, CD Woolard, PhD, B Essex, Virginia Dept of Health. EA Bresnitz, MD, New Jersey Dept of Health. JA Hayslett, PharmD, PM Dull, MD, EAS Whitney, MPH, DB Reissman, MD, TH Taylor, Jr., MS, B Plikaytis, MSc, N Rosenstein, MD, B Perkins, MD, DA Ashford, DVM, R Pinner, MD, National Center for Infectious Diseases, CDC.

Editorial Note:

The findings in this report suggest that the rates and causes of death among workers of the Brentwood mail facility during the 12 months after the anthrax attacks of 2001 were not different from those expected for this population. Although death certificate data might be subject to misclassification (3,4), the listed causes of death for the 11 workers do not raise suspicion of anthrax or mortality caused by adverse drug reactions.

If another anthrax attack were to occur, prevention of deaths would probably depend on heightened surveillance and rapid diagnostics to identify an attack and prompt prophylaxis with antibiotics and vaccination. Three types of surveillance are needed: 1) pre-event surveillance systems to detect the initial case of anthrax, which signals a new outbreak or release; 2) event surveillance to focus on continuous case-finding; and 3) postevent surveillance to identify any cases that might have been missed and morbidity and mortality associated with treatment or prophylaxis. In each stage of surveillance, the goals, priorities, and methods differ. Evaluation of unexplained deaths is an ongoing surveillance initiative that is part of CDC's Emerging Infections Program (5).

Monitoring of death rates among persons potentially exposed to B. anthracis spores during the anthrax attacks of 2001 continues; however, the onset of anthrax disease 2 years after the exposures is unlikely. Through December 2003, CDC, in collaboration with federal, state, and local partners, will continue to assess mortality among postal workers potentially exposed to B. anthracis at the USPS facilities and rates of adverse events among all 10,000 persons for whom >60 days of postexposure prophylaxis was recommended (6).

References

1. Dewan PK, Fry AM, Laserson K, et al. Inhalational anthrax outbreak among postal workers, Washington, DC, 2001. Emerg Infect Dis 2002;8:1066--72.
2. CDC. National Vital Statistics Report 2002;50(16):1--86.
3. Lloyd-Jones DM, Martin DO, Larson MG, Levy D. Accuracy of death certificates for coding coronary heart disease as the cause of death. Ann Intern Med 1998;129:1020--6.
4. Sington JD, Cottrell BJ. Analysis of the sensitivity of death certificates in 440 hospital deaths: a comparison with necropsy findings. J Clin Pathol 2002;55:499--502.
5. Hajjeh RA, Relman D, Cieslak PR, et al. Surveillance for unexplained deaths and critical illnesses due to possibly infectious causes, United States, 1995--1998. Emerg Infect Dis 2002;8:145--52.
6. CDC. Evaluation of postexposure antibiotic prophylaxis to prevent anthrax. MMWR 2002;51:59.

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