Updates
By Carol A. Kemper, MD, FACP, Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases; Santa Clara Valley Medical Center, Section Editor, Updates; Section Editor, HIV, is Associate Editor for Infectious Disease Alert.
Transmission of Herpes Zoster Virus
Sources: Mehta SK, et al. Varicella-zoster virus in the saliva of patients with herpes zoster. J Infect Dis. 2008; 197:654-657. Lopez AS, et al. Transmission of a newly characterized strain of varicella virus from a patient with herpes zoster in a long-term care facility, West Virginia, 2004. J Infect Dis. 2008;197;646-653.
In the health care setting, transmission of varicella zoster virus (VZV) from dermatomal herpes zoster lesions is generally felt to be insignificant, as long as the lesions are kept covered. While 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, the threat of nosocomial transmission from such persons is believed to be clinically significant only if the patient is immune-suppressed with possible increased amounts of virus present in respiratory secretions. For this reason, most infection control policies recommend contact precautions for patients with dermatomal zoster; most do not require isolation.
These two articles in the March 1, 2008 issue of Journal of Infectious Diseases may prompt reconsideration of these policies. In the first, the authors examined salivary samples for VZV DNA for a period of 2 weeks from 54 patients with herpes zoster presenting in a dermatomal distribution, all of whom received valacyclovir 1 gram orally three times daily for 7 days. VZV was detected in saliva collected from all 54 patients, all of whom had rash, on day 1, before initiation of therapy. In addition, VZV DNA was detected in the saliva and blood of one patient presenting with prodromal T12 dermatomal pain with no evidence of rash. She developed rash 3 days later, at which time she was treated.
The amount of VZV DNA (copy number) in saliva gradually decreased throughout the 14-day study period in 47 of 50 (94%) patients, although transiently increased in 3 persons before decreasing. Despite antiviral therapy, VZV DNA was still detectable in 18% of patients at day 14. Both the presence of, and the quantity of, VZV DNA in saliva strongly correlated with pain levels throughout the 2-week study. Infectious virus was cultured from one of two patients whose saliva was cultured in tissue culture, indicating that salivary VZV could result in transmission of infection. Although VZV has been detected in the saliva of patients presenting with Ramsey-Hunt Syndrome, it is curious that so many patients with (non-facial) dermatomal zoster had reactivation of virus in a location remote from their dermatomal reactivation.
Another group of authors report on the occurrence of a small outbreak of varicella in a long-term healthcare facility, following a case of herpes zoster 15 days earlier. Two of 56 residents of the facility, and 1 of 72 employees developed varicella. The index case was an 86-year-old lady with dementia who developed an uncomplicated case of zoster on her midback and abdomen, covering an area of about 14 x 21 cm. She was placed on contact precautions, and antiviral therapy was initiated 2 days later. By the 16th day, the lesions had completely crusted over.
Within 15-19 days of onset of the index case, three other individuals developed what appeared to be acute primary varicella. These included a 29-year-old employee who reported no other exposures to varicella and had changed the bed linens for the index case (the patient was not present at the time); a 49-year-old resident with cerebral palsy who required considerable staff assistance and could not move about the facility; and a 92-year-old resident who required total care, who also could not move about the facility. There was no known contact between the index case and the other two residents. Interestingly, all 3 cases of varicella were fairly mild. Analysis of IgG antibody levels and avidity indicated that the two younger cases were consistent with a primary immune response, whereas the 92-year-old probably had varicella reinfection.
Further laboratory investigation confirmed that 7 of 13 clinical specimens from the index case, and the 3 cases, were PCR-positive for VZV. In addition, 18 of 26 (69%) environmental samples taken from the bedframes, rooms, lockers, and community areas of the facility were also PCR-positive for VZV. VZV genotyping by DNA purification confirmed that the virus isolated from all four cases, and from the environmental samples taken from their rooms, was identical. In an interesting twist, the virus was a unique mosaic strain, with a marker characteristic for Oka vaccine-strain virus. It is not known whether this novel wild-type strain of VZV could be a recombinant from vaccine strain virus.
These two studies demonstrate that patients with dermatomal zoster may be infectious in a nosocomial setting, even 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. Salivary virus was detectable in about one-fifth of patients at two weeks, despite appropriate 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. This information is increasingly important as we develop a more highly immunized population where the incidence of varicella infection is low, and health care workers will be required to have current vaccination.
Bat rabies underestimated
CDC. Human Rabies — Minnesota, 2007. MMWR. 2008;57:460-462.
Only one case of human rabies was reported in the United States in 2007, in a 47-year-old man from northern Minnesota who died in October. He first presented in mid-September with paresthesias in his extremities about one month after handling a bat with his bare hands on the porch of his cabin. Within 10 days, he developed progressive respiratory failure, fever, and eventual coma. An initial MRI was negative, and the diagnosis was not initially suspected. It was only when subsequent MRIs showed progressive cervical spine and cranial T2 enhancement consistent with rabies that additional history from the family confirmed the bat exposure was obtained. Curiously, rabies virus antibodies were detected in CSF and serum, but no rabies virus antigen could be detected in skin biopsies, and attempts to amplify virus from saliva or skin were unsuccessful. (The only other case similar to this, where antibody was present but direct evidence of virus could not be confirmed, was the young Wisconsin teen who survived rabies in 2004.)
Rabies post-exposure prophylaxis was administered to 3 of 14 family contacts and 51 of 524 health care workers with possible exposure to the patient's saliva. A search of the cabin failed to find any evidence of bats, but the public health department determined that a bat bite was the most likely source for infection.
Bats are responsible for at least 28% of rabies cases in the United States, although some data suggest it may be closer to half. Most of these cases occur in the late summer and fall months, when exposure to bats is more common. Bats and skunks are the only source of rabies in Minnesota, although this article states "the significance of bat exposure often is ignored".
This alert had special significance for me growing up in northern Minnesota. As a kid, we used to watch the bats by the hundreds — swoop, swoop, over the lake, silently at dusk, eating mosquitoes as we dangled our feet at the end of the dock, watching the last bit of summer sun settle for the night on the horizon. As a kid, we'd even shoot arrows at bats hanging from the eaves, thinking it good target practice. And more then once, someone in the house had to take a broom or a tennis racket to one loose in the cabin.
If you touched one, mother made you wash your hands. One year, a group of bats set up housekeeping in the mainbeam at the cabin, and we used to lie in bed at night listening to them crawl around above us; bat urine would drip down and crystallize on the 12" beam. Once they found a home, they were virtually impossible to get rid of. The worst experience was my mother and I arriving late one night to the cabin to find a colony of bats roosting in the wood burning stove; undaunted, because we needed heat, we lit the stove. The next morning, I had to pluck more than 30 little burnt bodies from the ashes. While we were (peripherally) aware of the threat of rabies from bats, we'd actually never heard of a case, and the threat seemed just one of many to folks trying to carve out a home amongst all kinds of other wildlife. Frankly, we were more concerned about the bears.
In the health care setting, transmission of varicella zoster virus (VZV) from dermatomal herpes zoster lesions is generally felt to be insignificant, as long as the lesions are kept covered.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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