Hospital
Infection
Control
for Varicella
Zoster
Virus
Infection
Martin C. Myers, MD, Dorothy A. Rasley, RN, and
Walter J. Hierholzer, MD
From the Department of Pediatrics and Program of Epidemiology, University of Iowa Hospitals and Clinics, Iowa City
ABSTRACT. More than 500 hospital employees and 209 patients were exposed to varicella zoster virus (VZV) as a consequence of 22 uncontrolled hospital introductions that occurred over a period of 34 months. Five introduc-tions of vancella were by hospital employees who ac-quired the infection outside the hospital. Successful in-fection control of VZV requires an accurate definition of the susceptible population and the limitation of transmis-sion. Individuals with prior VZV infection are epidemio-logically not at risk for developing clinical illness. Sero-logic screening of hospital employees with uncertain prior VZV history is effective in identifying those at risk of developing the infection. A prior history of intimate ex-posure to VZV does not imply immunity in the absence of clinical illness. Pediatrics 70: 199-202, 1982; varicella
zoster virus, infection control.
Varicella zoster virus (VZV) infections are gen-erally uncomplicated and self-limited illnesses. Al-though the risk of acquiring varicella is less after
exposure to herpes zoster than after exposure to
varicella,’ the course of the infection is indistin-guishable.2 In addition, the contagious nature of VZV infections for susceptible individualst and the severe illness that may occur in immunocomprom-ised hosts4 create special problems for hospital in-fection containment.
Transmission of VZV is most efficient by direct contact,5 although airborne spread without direct contact has been documented.6’7 The natural portal of entry is probably the nasopharynx.8
Infection control procedures are designed to pre-vent the spread of microorganisms among patients, hospital personnel, and visitors. Inasmuch as agent
Received for publication June 1, 1981; accepted Aug 3, 1981.
Reprint requests to (M.G.M.) Division of Infectious Diseases, Children’s Hospital Medical Center, Elland and Bethesda Aye, Cincinnati, OH 45229.
PEDIATRICS (ISSN 0031 4005). Copyright © 1982 by the American Academy of Pediatrics.
and host factors are difficult to control, interruption of the chain of infection is directed primarily at
transmission. To interrupt transmission effectively
it is necessary to define the susceptible population and to minimize the exposure of susceptible individ-uals. Patients with common contagious diseases, such as varicella, rarely require hospital admission
unless some complication develops. However,
im-munosuppressed patients may develop reactivation infection while hospitalized, some patients may
un-knowingly be incubating varicella, and some
pa-tients, particularly hospital employees, may be ex-posed without knowledge of their immune status. We report an evaluation of our infection control policies for VZV during 22 introductions over a 34-month period.
MATERIALS AND METHODS
Facilities
The University of Iowa Hospitals and Clinics is an 1,100-bed, general hospital facility, providing tertiary care services for the state of Iowa. Although most pediatric patients receive their care on pedi-atric wards, older children may be admitted to any
specialty service. Because of the referral nature of
the hospital, almost all wards contain patients who are immunocompromised by either disease or drug therapy.
Infection Control Policies
On admission to the hospital, all pediatric
pa-tients are screened for exposure and immunization
histories by the admitting nurse. Children who are
200 VARICELLA ZOSTER VIRUS INFECTION and those with varicella are placed in strict isolation until 28 days following exposure or until all lesions are crusted. Strict isolation requires a private room with the door kept closed, and gowns, masks, and
gloves for all persons entering the room. Hand
washing is required on entering and exiting the
room, and all articles leaving the room must be
wrapped in double bags prior to terminal steriliza-tion.
When an introduction of VZV occurs within the
hospital, the patient is placed in strict isolation and all contacts are identified by the nurse epidemiolo-gist. All contacts are screened for their susceptibil-ity to VZV. Patients who have had varicella or herpes zoster are considered immune. Newborns
and young children who have not been infected
with varicella are considered susceptible. Patients who have been exposed and who may be susceptible are discharged, if possible, within eight days. If it is not possible to discharge the patients, they are placed in strict isolation eight days after exposure.
Hospital employees who are exposed and whose
history of previous VZV infection is uncertain are
tested serologically for immunity to VZV. Those
employees who are found to be immune
serologi-cally are allowed to continue to work. Personnel who are found to be serologically susceptible are given paid sick leave from eight days after exposure until after varicella lesions have crusted or until 28 days following exposure. Immunocompromised pa-tients who are susceptible to VZV are administered
immune prophylaxis with either zoster immune
globulin or, if not available, zoster convalescent
plasma. When multiple patients have had a
com-mon source exposure to VZV, isolation has been
implemented employing cohorts.
Serologic Methods
Serologic immunity to VZV has been assayed by
fluorescent antibody to membrane antigen
(FAMA)8’9 or by an enzyme-linked immunosorbent
assay (ELISA).9 Sera tested by both methods had
a high degree of correlation.9 When a discrepancy occurred, the tests were repeated and the individual was treated as serologicafly susceptible to VZV. Sera were tested at dilutions of 1:4 by FAMA or 1:5
by ELISA.
RESULTS
When active VZV infections were detected, most individuals were appropriately isolated according to our usual hospital infection control policies. How-ever, in the interval from April 1978 through Jan-uary 1981 we had 22 uncontrolled introductions of
VZV into our hospital population. Only four of
these were episodes of zoster occurring in hospital-ized patients. There were seven adults with van-cella; two were obstetric patients. Five adults with varicella were hospital employees whose exposure
occurred outside the hospital, and they had not
realized they were susceptible, although none had a prior history of varicella or zoster. The remaining 11 children were either incubating varicella or had
varicella at the time of admission and were not
appropriately isolated. These 1 1 children were ad-mitted to pediatrics (two children), a surgical sub-specialty (seven children) , internal medicine (one
child), and a psychiatric chronic care ward (one child). More than 500 hospital employees and 209
patients were exposed to VZV during the short
periods prior to detection of the introductions. Sec-ondary cases of vanicella within the hospital
oc-curred only on the psychiatric ward, which was
closed to admissions of VZV-susceptible patients until 28 days after the last case of varicella.
Varicella occurred only in susceptible individuals,
all of whom were detected and isolated by our
infection control procedures (Table). Vanicella did not occur in any of the 527 individuals with a history
of preceding VZV infection, including the 49 we
tested serologically. Sixty-eight hospital employees and ten chronically hospitalized patients were eval-uated serologically for immunity to VZV because of no, or uncertain, preceding history of VZV infection.
Forty-one (53%) of these individuals were found to
be susceptible to VZV, and of 1 1 who subsequently developed clinical varicella, four were nurses. Thirty-six hospital employees with no history of
preceding VZV infection had titers of 1:4 and
continued working. None of these developed van-cella.
Sixteen individuals gave a history of previous
close household exposure to VZV without having
TABLE. Varicella Zoster Virus
Among Hospital Contacts
(VZV) Immunity
No. No. No. Who Tested Sero- Developed
nega- Varicellat
tive*
History of prior infection 49 0 0
Uncertain prior history 78 41 11
History of prior household 16 9 4
exposure
* Fluorescent antibody to membrane antigen (FAMA)
<1:4 and/or enzyme-linked immunosorbent assay (ELISA) <1:5.
t Varicella occurred only in seronegative individuals.
1:
Of 527 individuals who had history of prior VZV infec-tion and were identified epidemiologicaily, none devel-oped varicella.developed clinical illness. Of these, nine (56%) were found serologically to be susceptible and four of the nine developed clinical varicella after exposure.
DISCUSSION
Successful infection control for VZV requires the prevention of introduction, or the immediate isola-tion, of infectious patients and an accurate
defini-tion of the exposed susceptible population.
Al-though we have been moderately successful in lim-iting hospital admissions of children who are incu-bating or who have varicella by obtaining an ad-mission infectious diseases history, it has not been possible to prevent all hospital introductions of VZV. Thus, zoster may occur among hospitalized patients, patients with VZV infections may not be immediately detected, and susceptible employees may unwittingly introduce VZV from sources out-side the hospital. For example, one introduction was traced to a pediatric blood gas technician who
developed vanicella after exposure to a family
con-tact.
Protection against subsequent VZV infection has been associated with reactive serology when meas-ured by a sensitive assay such as FAMA,’#{176} ELISA,9
complement-enhanced neutralization,” and
ra-dioimmunoassay.’2 This is supported by our obser-vation that seroreactive individuals (as determined by FAMA or ELISA) did not develop infection after hospital exposure. Less sensitive assays, such as classic virus neutralization and complement fixa-tion, may be as specific but wifi detect immune individuals less often.
Although nearly all (96%) susceptible family con-tacts of varicella develop clinically apparent infec-tion,’ the history of close household exposure
with-out clinical illness does not imply immunity to
varicella. Thus, nine of 16 such individuals were found susceptible, and four of the nine developed
varicella. For example, one nurse who had been
exposed as a child to three siblings with varicella developed chickenpox after exposure to herpes zos-ter. She had contact with 58 patients, 32 members of the nursing staff, and five clinical staff members on the first day of varicella.
The performance of varicella serologic tests on hospital personnel who have no definitive prior history of VZV infection is cost effective. After exposure, 36 employees, including eight physicians, were determined “safe” for patient contact. Assum-ing 15 days lost from work for these employees, the determination of immunity saved an estimated 540 workdays. Had all 68 hospital employees without history of prior VZV infection been allowed to con-tinue to have patient contact, we would have had
four additional introductions of VZV by individuaLs with multiple opportunities for nosocomial spread.
History of prior infection with VZV should be
obtained from all hospital personnel prior to em-ployment. Individuals with no or uncertain prior infection should be screened serologically for im-munity. VZV-susceptible employees should be aware of their potential to acquire and spread VZV within the hospital.
IMPLICATIONS
1. Hospital personnel should be screened for
im-munity to VZV by history, and if uncertain, by
serologic testing. Susceptible employees should be aware of the potential to acquire and spread VZV.
2. Pediatric patients should be screened at ad-mission for recent exposure or illness due to VZV. Patients with vanicella, herpes zoster or those in-cubating vanicella should either not be admitted to the hospital or should be isolated immediately.
3. When an introduction of VZV inadvertently occurs within the hospital, the patient should be placed on strict isolation or discharged from the hospital, and all susceptible contacts must be iden-tifled and isolated.
4. Immunity is highly probable in individuals with known prior infection with VZV, but cannot be assumed in adults, including those with prior intimate exposure but without a history of clinical illness.
ACKNOWLEDGMENTS
This work was supported by US Public Health Service grant Al 13627 and by the University of Iowa Hospital Program in Epidemiology.
We thank Helen Duer for technical assistance.
REFERENCES
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2. Hope-Simpson RE: Studies on shingles: Is the virus ordinary
chickenpox virus? Lancet 2:1299, 1954
3. Ross AH: Modification of chickenpox in family contacts by
administration of gamma globulin. N Engl J Med 267:369,
1962
4. Feldman 5, Hughes WT, Daniel CB: Varicella in children
with cancer: Seventy-seven cases. Pediatrics 56:388, 1975
5. Zoster immune globulin. Morbidity Mortality Weekly Rep
25:211, 1976
6. Habel K: Mumps and chickenpox as air-borne diseases. Am J Med Sci 209:75, 1945
7. LeClair JM, Zaia JA, Levine MJ, et al.: Air-borne transmis-sion of chickenpox in a hospital. N EngI JMed 302:450, 1980
8. Myers MG: Viremia caused by varicella-zoster virus:
Asso-ciation with malignant progressive varicella. J Infect Dis
140:229, 1979
9. Shanley J, Myers MG, Edmond B, et al: An enzyme linked
immunosorbent assay for detection of antibody to varicella
202 VARICELLA ZOSTER VIRUS INFECTION
10. Williams V, Gershon A, Brunell PA: Serologic response to Infect Dis 139:432, 1979
varicella membrane antigens measured by indirect immu- 12. Friedman MG, Leventon-Kriss 5, Sarov I: Sensitive solid
nofluorescence. J Infect Di.s 130:669, 1974 phase radioimmunoassay for detection of human immuno-11. Grose C, Edmond BJ, Brunell PA: Complement-enhanced globulin G antibodies to varicella-zoster virus. J Clin
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PSYCHOLOGY OF PREFERENCES
Recent investigations of the psychology of preferences have demonstrated several intriguing discrepancies between subjective and objective conceptions of decisions. For example, the threat of a loss has a greater impact on a decision than the possibility of an equivalent gain. Most people are also very sensitive to the difference between certainty and high probability and relatively insensitive to intermediate gradations of probability. The regret associated with a loss that was incurred by an action tends to be more intense than the regret associated
with inaction or a missed opportunity. These observations and others of a
similar character contribute to the understanding of how people make decisions and to the elucidation of some puzzles of rational choice . ...
We asked a large number of physicians to consider the following problem: Imagine that the U.S. is preparing for the outbreak of a rare Asian disease, which is expected to kill 600 people. Two alternative programs to combat the disease have been proposed. Assume that the exact scientific estimates of the consequences of the programs are as follows: If Program A is adopted, 200 people will be saved. If Program B is adopted,
there is a 1/3 probability that 600 people will be saved and a 2/3 probability that no people will be saved. Which of the two programs would you favor.
The majority response to this problem is a risk-averse preference for Program
A over Program B.
Other respondents were presented with the same problem but a different
formulation of the programs: If Program C is adopted, 400 people will die. If Program D is adopted, there is a 1/3 probability that nobody will die and a 2/3 probability that 600 people will die.
The majority choice in this problem is risk-seeking: the certain death of 400 people is less acceptable than a 2/3 chance that 600 people will die.
It is easy to see that the two versions of the problem describe identical outcomes. The only difference is that in the first version the death of 600 people is the normal reference point and the outcomes are evaluated as gains (lives saved), whereas in the second version no deaths is the normal reference point and the programs are evaluated in terms of lives lost.
Submitted by Student
