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Increasing Herpes Zoster Among Veterans: An Unintended Consequence of the VZV Vaccine?
Abstract & Commentary
By Robert Muder, MD, Hospital Epidemiologist, Pittsburgh VA Medical Center, Section Editor Hospital Epidemiology, is Associate Editor for Infectious Disease Alert.
Synopsis: Between 2000 and 2007, the annual incidence of herpes zoster among veterans increased from 3.10/1000 to 5.22/1000. The increase was confined to veterans over 40 years of age. The authors postulate that lack of exposure to varicella, due to widespread immunization of children with VZV vaccine, may be a contributing factor.
Source: Rimland D et al. Increasing Incidence of herpes zoster among veterans. Clin Infect Dis. 2010;20:1000-1005.
The Veterans Health Administration maintains a national automated information system (DSS) that contains hospital discharge and outpatient data for the entire system. It was fully operational in 1999. Investigators at the Atlanta VA Medical center identified unique patient encounters for herpes zoster during the period of October 1999 through September 2007 (federal fiscal years 2000-2007). Inpatient and outpatient data were assessed, as were patient age and sex. Both primary and secondary diagnoses of herpes zoster were included. An individual patient could be included only once per year so that multiple visits for a single episode would not be counted.
The investigators found a steady increase in incidence of herpes zoster from 3.10 episodes per 1,000 in FY 2000 to 5.22 per 1,000 in FY 2007, a 68% increase. The increase was seen only among veterans older than 40 years. They then performed a validation study by reviewing all patients diagnosed with herpes zoster at the Atlanta VA for the same period. All cases were reviewed by an experienced infectious disease specialist, who found that 56% of cases represented an acute episode of herpes zoster. The majority of the remainder was a remote episode or a diagnosis of post-herpetic neuralgia. The increase in confirmed zoster diagnoses over the period was 75.6%. The increase was significant even when patients with HIV infection, malignancy, and chemotherapy were excluded.
This study shows a rather striking increase in varicella zoster over a seven-year period among veterans. This investigation was possible because the Veterans Health Administration maintains a national automated information system that draws data from the VA's nationwide system of computerized medical records. Although the validation study in Atlanta found that only 56% of diagnoses of varicella zoster represented a new episode, the increase in the rate of zoster was similar to the national data. Because the VA medical record system is standardized, the Atlanta findings are highly likely to be representative of the system as a whole. One potential weakness is that patients use care outside of the VA as well, and some episodes of varicella zoster would not be captured. However, it seems unlikely that the change in rates was due to a large shift of veterans with zoster into the VA healthcare system. There is no evidence that the prevalence of diseases associated with immune dysfunction, such as HIV, is increasing among veterans.
This reason for this apparent increase in varicella zoster in not clear. The authors note that varicella immunization was implemented in the United States in 1995. Exposure of adults to cases of varicella elicits an immune response in those with latent varicella zoster infection, and this may provide some degree of protection against the later development of zoster. Some investigators have, in fact, predicted an increase in herpes zoster following the implementation of mass varicella immunization.1
It should be noted that other studies of the incidence of zoster over time have shown inconsistent results.2 It would be quite useful to confirm an increase in varicella zoster among the general population. Zoster causes considerable morbidity, particularly among the elderly. A zoster vaccine (Zostavax, Merck) is available and recommended for the prevention of herpes zoster in those 60 and older.3 The vaccine significantly decreases the incidence of zoster and post-herpetic neuralgia, a particularly unpleasant sequela. If the rate of varicella zoster is indeed increasing, more widespread administration of the zoster vaccine is warranted.