Gay, Nigel J.; De Serres, Gaston; Farrington, Paddy; Redd, Susan B. and Papania, Mark J.
Assessment of the status of measles elimination from reported outbreaks: United States, 1997-1999.
The Journal of Infectious Diseases, 189(Suppl 1) S36-S42.
The status of measles elimination is best summarized by evaluation of the effective reproduction number R; maintaining R<1 is necessary and sufficient to achieve elimination. Previously described methods for estimating R from the sizes and durations of chains of measles transmission and the proportion of cases imported were applied to the measles data reported for the United States in 1997-1999. These comprised 338 cases, forming 165 chains of transmission, of which 43 had >1 case. One hundred seven cases were classified as importations. All 3 methods suggested that R was in the range 0.6-0.7. Results were not sensitive to the minimum size and duration of outbreak considered (so long as single-case chains were excluded) or to exclusion of chains without a known imported source. These results demonstrate that susceptibility to measles was beneath the epidemic threshold and that endemic transmission was eliminated.
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