The time available to implement successful control measures against epidemics was estimated. Critical response time (CRT), defined as the time interval within which the number of epidemic cases remains stationary (so that interventions implemented within CRT may be the most effective or least costly), was assessed during the early epidemic phase, when the number of cases grows linearly over time. The CRT was calculated from data of the 2001 foot-and-mouth disease (FMD) epidemic that occurred in Uruguay. Significant regional CRT differences (ranging from 1.4 to 2.7 days) were observed. The CRT may facilitate selection of control measures. For instance, a CRT equal to 3 days would support the selection of measures, such as stamping-out, implementable within 3 days, but rule out measures, such as post-outbreak vaccination, because intervention and immunity building require more than 3 days. Its use in rapidly disseminating diseases, such as FMD, may result in regionalized decision-making.

Cross-reactivity indices (CRIs) of 28 isolates of Moraxella bovis recovered from outbreaks of infectious bovine keratoconjunctivitis in Argentina (A, 11 isolates), Brazil (B, 7), and Uruguay (U, 10) between 1983 and 2000 were estimated. Hyperimmune sera were produced in rabbits and antibody titres determined with each isolate. Isolates showing CRIs3 70 were placed in the same group. Group I had 13 isolates (A, 1; B, 6; U, 6); group II had 6 isolates (A, 4; U, 2); groups III, IV, and V had 2 isolates each, recovered in Argentina; group VI had 2 isolates, from Uruguay; and group VII had 1 isolate, from Brazil. The CRIs3 70 between vaccine strains and isolates recovered before and after 1990 were 58% and 42%, 50% and 50%, and 33% and 67% with vaccine strains 2419, 2358, and 2439, respectively. Isolate 273, from Uruguay, showed CRIs > 70 with 78% of the isolates and is recommended as the vaccine strain.