Ascertaining the 2004–2006 HIV type 1 CRF07_BC outbreak among injecting drug users in Taiwan

OBJECTIVE: To ascertain the explosive 2004–2006 outbreak of HIV-1 CRF07_BC among intravenous drug users (IDU) in Taiwan, which more than doubled the total number of reported HIV cases in less than 3 years, resulting in a 45-fold increase in cumulative IDU/HIV cases and a 40-fold increase in previously seldom-reported female IDU/HIV cases. METHODS: A mathematical model was utilized to fit the monthly case data, in order to estimate the turning points (peak incidence) and the reproduction number R of the outbreak. Furthermore, correlation analysis was carried out to assess the correlation between infections among the male and female IDUs. RESULTS: Model fit revealed a two-wave epidemic during April 2004–March 2007. The larger second wave started shortly after May 2005 and peaked in October 2005 before gradually subsiding. R was estimated to be 3.15 (3.14–3.16) and 27.21 (26.73–28.05) for the two respective waves. The time series of monthly differences in male and female case data were found to be most significantly correlated at lag 0 (i.e., r > 0.7) with r = 0.906 and 0.804, respectively in each direction. The Granger causality test indicated that the male time series caused the corresponding female time series with a lag of 2 months or less. CONCLUSIONS: The modeling results revealed the presence of a small first wave in 2004, before an explosion of cases after May 2005. Furthermore, a harm reduction program implemented in August 2005 contributed to the downturn in the epidemic after October. Correlation results also suggest that the upsurge in male HIV cases led to the subsequent drastic surge in female cases.