1. See www.cdc.gov/mmwr/indexbt.html.
2. Inglesby T. V., et al., J. Am. Med. Assoc. 281, 1735 (1999).
3. Jernigan J. A., et al., Emerg. Infect. Dis. 7, 933 (2001).
4. The likelihood function is the product of factors from three groups. For the i th group x i is observed number of cases and n i is number of cases that would have occurred had AP not been used. Factors for clusters with known exposure date are binomial likelihoods nixi [ F ( T i )] x i [1− F ( T i ] n i −x i where T i is the time interval between exposure and AP. The likelihood factor for the group with unknown exposure date ( E ) is nixi [1−F(P−E)]ni−xi ∏j=1xi f(tj−E) where P is the date of AP t j is the onset date of symptoms for the j th case and f is the incubation density. The profile likelihood for total N = n 1 + n 2 + n 3 is obtained by maximizing over E n 1 and n 2 .
5. Meselson M., et al., Science 266, 1202 (1994).