The changing landscape of antiviral treatment of herpes zoster: a 17-year population-based cohort study

BACKGROUND Herpes zoster (HZ) is a common viral disease that produces a painful vesicular rash. Early use of antiviral medications is recommended, as it reduces pain and speeds healing. A population-based observational study was conducted to evaluate the changing burden of HZ in the province of Manitoba (Canada) over a period of 17 years. METHODS Administrative health care data including medical and hospital records were examined, and International Classification of Diseases, Ninth Revision, Clinical Modification and International Classification of Diseases, Tenth Revision, Clinical Modification codes were used to identify episodes of HZ between April 1, 1997 and March 31, 2014 in persons aged 20 or over. Annual age-adjusted incidence and hospitalization rates were calculated. Prescription records of HZ-diagnosed persons for acyclovir, valacyclovir, and famciclovir were used to calculate the rates and costs of antiviral treatment. RESULTS There were 73,893 identified cases of HZ and 1,245 HZ-related hospitalizations between 1997 and 2013. Of these episodes, 42,270 (57.2%) were treated with antiviral medications at a total cost of $4,708,065 (CAD). The age-adjusted incidence of HZ rose from 4.67/1,000 person years in 1997/1998 to 5.67/1,000 person years in 2013/2014, a 21.9% increase. Antiviral treatment rates increased from 41.7% to 66.2% of all diagnosed episodes. Mean treatment costs per episode dropped from $127.29 in 1997/1998 to $56.06 in 2013/2014, primarily due to the introduction of generic antiviral medications. The total cost of antiviral treatment peaked in 2005/2006 at $329,935 and dropped steadily thereafter to $223,973 in 2013/2014. HZ-related hospitalization rates decreased from 3.1% to 0.9%. CONCLUSION While both the incidence of HZ and the rates of antiviral treatment have risen substantially, the economic burden from antiviral treatment has been decreasing since a peak in 2005/2006 and was only 3.2% higher in 2013/2014 than in 1997/1998. This drop in cost is attributed to the introduction of generic antiviral drugs.