Investigations suggest that the latest case of inhalation anthrax in the United States may have arisen from an envelope that was cross contaminated by contact with other letters containing Bacillus anthracis.
This case arose in a 94 year old resident of Oxford, Connecticut. She became unwell on 13 November with fever, cough, weakness, and muscle aches. She was admitted to hospital on 16 November but deteriorated despite treatment and died on 21 November. B. anthracis was isolated from blood cultures and tissue specimens taken at autopsy. The strain was indistinguishable from those isolated from other recent cases of anthrax. This brings the total to 22 cases of anthrax related to recent deliberate releases: 11 cases of inhalation disease and 7 confirmed and 4 suspected cases of cutaneous disease.
With the exceptions of the Connecticut case and an earlier case of inhalation disease in a hospital worker in New York, cases of anthrax related to deliberate releases have arisen in association with media companies or postal facilities. Environmental and epidemiological findings indicate that pulmonary infection has occurred from aerosols generated by opening or handling letters known to contain B. anthracis in a fine powder form.
The Connecticut and New York inhalation cases did not have contact with known contaminated letters. The Connecticut patient lived alone in a rural area and was largely housebound. Tests on environmental samples from her home and the places she visited in the 60 days before onset of symptoms have proved negative. In addition, nasal swabs from friends and relatives who may have shared common exposures have not detected B. anthracis.
Although there is no evidence that the Connecticut patient was exposed directly to a known contaminated letter, environmental tests suggest that she may have been infected through the spread of contamination in the US postal system. B. anthracis has been detected on three sorting machines at the postal distribution centre that delivered mail to the patient’s home. Mail flow investigations have revealed that this centre received letters from the postal facility in Hamilton, New Jersey, where the anthrax letters sent to two US Senators were initially processed, and which has been shown to be extensively contaminated. B. anthracis has also been detected on an envelope sent to an address 4 miles from the patients home, and sorting records from Hamilton show that this was processed by the same machine that had processed one of the anthrax letters less than a minute previously.
Some 85 million pieces of mail were processed by postal facilities in New Jersey (NJ) and the District of Columbia (DC) in the days after the anthrax letters sent to US Senators and before they were closed. Envelopes passing through these facilities could have been cross contaminated and, in turn, could have contaminated mail processing equipment or other envelopes. Active surveillance has, however, not identified further cases of inhalation anthrax among 10.5 million residents in NJ, DC, and surrounding areas that received mail from these facilities. This prolonged active surveillance of such a large population suggests that if there is a risk of inhalation anthrax associated with cross contaminated envelopes, then it is very low.