Abstract
Of 53,633 suspected dengue cases reported to a passive dengue surveillance system in Puerto Rico during 2005-2010, 949 individuals were reported on more than one occasion and 21 had laboratory-confirmed dengue on two separate occasions. Median time between illness episodes was 2.9 years (range: 62 days-5.3 years). Seventeen (81%) individuals with sequential episodes of dengue were male, and seven (33%) were adults. All 21 individuals experienced one episode and seven (33%) individuals experienced both episodes during a large epidemic that occurred in 2010. These observations show that heterotypic dengue virus immunity that protects against illness may have considerable variability but typically does not last longer than 3 years.