A Pox on You!
By Carol A. Kemper, MD, FACP
Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases, Santa Clara Valley Medical Center
Dr. Kemper does research for Abbott Laboratories and Merck. This article originally appeared in the July issue of Infectious Disease Alert.
Source: Viner K, et al. Transmission of varicella zoster virus from individuals with herpes zoster or varicella in school and day care settings. J Infect Dis 2012;205:1336-1341.
SUSPICIONS HAVE PREVIOUSLY BEEN RAISED ABOUT THE higher than expected risk of transmission of varicella zoster virus (VZV) from patients with herpes zoster (shingles) under ordinary circumstances. VZV has been detected in ventilation units used for patients hospitalized with zoster, suggesting that airborne virus is occasionally found in the rooms of patients with dermatomal zoster. Salivary samples for VZV DNA from patients with dermatomal zoster are frequently positive, and VZV DNA can be found in 18% of salivary samples at 2 weeks of antiviral therapy. Potentially infectious varicella virus was even found in the saliva of a young woman with prodromal pain who had not yet developed dermatomal lesions. Another report documented the occurrence of a small outbreak of varicella in a long-term health care facility, following a case of herpes zoster 15 days earlier. Laboratory investigation confirmed that 18 of 26 (69%) environmental samples taken from the bedframes, rooms, lockers, and community areas of the facility were PCR-positive for VZV identical to that isolated from four cases.
These reports demonstrate that patients with dermatomal zoster may be infectious in a nosocomial setting, especially to patients with a prior history of varicella with waning immunity. Virus may be shed or aerosolized from zoster lesions, and infectious virus may be present in the saliva of patients with active zoster.
Viner and colleagues examined the risk of acquisition of VZV from persons with dermatomal zoster in schools and day care facilities in their community from 2003-2010.
They focused on cases of varicella occurring within 10-21 days of a reported case of dermatomal zoster or a sporadic case of varicella within the same facility. A sporadic case of varicella was defined as occurring > 6 weeks after or at least 10 days before another case of varicella. The cases were stratified based on vaccine status and disease severity. Tertiary cases occurring within 10-21 days of a secondary case were also included.
During the 8-year period of observation, 2296 cases of herpes zoster and varicella were reported by schools or day cares. Of these, 1648 were considered primary cases, including 1358 cases of sporadic varicella. For the herpes zoster cases, 27 (9%) were associated with the occurrence of 84 secondary cases of varicella within the same institution; 70% of these were considered mild. In contrast, 15% of the sporadic cases of varicella were associated with the occurrence of 564 cases of secondary varicella within the same institution. About 72% of these were considered mild. Most of the children (> 90%) with secondary varicella had previously received at least one dose of vaccine.
Thus, the risk of secondary VZV infection appeared similar, regardless of whether the index case had dermatomal zoster or varicella. In addition, transmission from either a case of zoster or varicella similarly resulted in a single case of varicella about half the time, in 2-4 secondary cases about one-third the time, and outbreaks with multiple infections 14% of the time. One case of shingles was associated with 30 secondary varicella cases over a 3-month period at one facility; and, at another facility, a single case of chickenpox resulted in 35 secondary cases over a 7-month period.
Environmental samples collected from doorknobs, computers, and desks were positive for VZV DNA from three of nine elementary schools surveyed.
The authors believe the gradual reduction in naturally occurring varicella infection as the result of pre-school vaccination is leaving an environmental niche for increased transmission from persons with dermatomal zoster. It is likely that this low-grade transmission has existed forever, resulting in natural repriming of individuals with pre-existing immunity at low risk for symptomatic reinfection — only now it is occurring in previously vaccinated children with obviously less robust immunity.
At a minimum, this represents a low-cost approach to repriming immunity at relatively low risk, in contrast to broad revaccination booster programs. All I know is that I am a whole lot more confident in my own naturally-acquired immunity.
Transmission of varicella zoster virus from individuals with herpes zoster or varicella in school and day care settings.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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