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Office of Epidemiology May 2002 Utah Department of Health

Hantavirus Pulmonary Syndrome

Since surveillance began in 1993, twenty-one cases of Hantavirus Pulmonary Syndrome (HPS) have been identified in Utah with a 33% case fatality rate. Of Utah cases, 67% have been male and 33% female. The mean age of confirmed cases in Utah is 35 years (range: 19 to 67 years). Cases have been identified in 9 Utah Counties (Figure 1). As of April 2002, a total of 313 cases of Hantavirus Pulmonary Syndrome (HPS) have been reported in the United States with a 37% case fatality rate. Of persons ill with HPS, 60% have been male, 40% female. The mean age of confirmed case patients nationwide is 37 years (range: 10 to 75 years).

Three cases of Hantavirus Pulmonary Syndrome have occurred in Utah in 2002. The first, a 25-year-old Wayne County resident, was hospitalized from April 26 to May 24. Initial interviews with family and friends indicated that the patient had history of camping and working in the outdoors. No specific rodent exposure was noted. The complete investigation is being conducted by Central Utah Health District. The second HPS case was a 22-year-old Salt Lake County resident. The patient was hospitalized from May 10-17. Investigation is being conducted by Salt Lake Valley Health Department. The third case, from Iron County was hospitalized on June 2. Illness developed rapidly and the patient expired on June 2. The investigation is being conducted by Southwest Utah Health District. Each time new cases are identified, awareness is heightened among the medical community as well as the general public regarding the seriousness of HPS.

Due to the rapid onset of shock and respiratory failure, early recognition of the illness is critical in reducing the risk of mortality. HPS begins four days to six weeks after exposure to infected rodents or their excreta, although not all patients give a history of rodent exposure. All patients experience a prodromal phase with fever, chills and myalgias, persisting for 1 to 7 days before progression to the cardiopulmonary phase. Pain in the legs and back can be very severe during the hantavirus prodrome. Many patients also experience nausea, vomiting and diarrhea. Cough and other upper respiratory symptoms are not present at the onset of the prodromal phase but instead begin hours before the onset of the noncardiogenic pulmonary edema and cardiogenic shock.

Since it is difficult to clinically distinguish between the prodrome of HPS and that of many other viral and bacterial infections, the liberal use of the complete blood count (CBC) with differential and platelet count is recommended. A low platelet count (<150,000 in 98% of cases; <130,000 in 92%) is the only CBC abnormality consistently seen during the prodromal phase. All HPS cases eventually have platelets <100,000. Other nonspecific lab results suggestive of prodromal HPS include elevated LDH, elevated AST, and reduced serum bicarbonate. Patients with symptoms consistent with early HPS but with platelets counts of >150,000 should be advised to return to the clinic in 24 hours for re-evaluation. The transition from hantavirus prodrome to respiratory failure occurs 4 to 12 hours after onset of cough and shortness of breath. With the onset of pulmonary edema, the CBC now shows thrombocytopenia, elevated hematocrit, leukocytosis with circulating myelocytes, promyelocytes, and immunblasts, recognized as large atypical lymphocytes with deep blue cytoplasm. Patients with suspected HPS (thrombocytopenia and compatible clinical picture) should be transported to a critical-care unit as early as possible. All patients with suspected HPS should be under respiratory isolation until the diagnosis of HPS is confirmed by serology.

The following are clues for finding the rare HPS case among thousands of flu syndromes:

1- Flu syndrome presents without rhinorhea, otitis, sinusitis, congestion.

2- Nausea, vomiting, diarrhea, abdominal pain are often severe

3- Cough does not begin on the first day of symptoms, but generally after two or more days and heralds the onset of pulmonary edema

4- During prodrome, thrombocytopenia is the only lab sign.

5- A rapidly falling platelet count helps distinguish HPS, sepsis, plague, tularemia, etc., from benign causes.

Clinically, a case is defined as an illness characterized by one of more of the following clinical features:

  • A febrile illness (i.e., temperature > 101.0 F [>38.3 C]) characterized by bilateral diffuse interstitial edema that may radiographically resemble acute respiratory disease syndrome (ARDS), with respiratory compromise requiring supplemental oxygen, developing within 72 yours of hospitalization, and occurring in a previously health person.

  • An unexplained respiratory illness resulting in death, with an autopsy examination demonstrating noncardiogenic pulmonary edema without and identifiable cause.

  • Laboratory criteria for diagnosis include:

  • Detection of a hantavirus-specific immunoglobulin M or rising titers of hantaviurs-specific immunoglobulin G.

  • Detection of hantaviurs-specific ribonucleic acid sequence by polymerase chain reaction in clinical specimens.

  • Detection of hantavirus antigen by immunohistochemistry.

HPS has emerged as a new disease since identified in the spring of 1993. Even though it is considered a new viral zoonosis, retrospective case-finding has indicated that it is not new to the United States. The retrospective diagnosis of case-patients from as early as the 1959 Utah case reveals that human hantavirus infections resulting in HPS went unrecognized until May 1993.

The human-rodent interaction and the identification and characterization of environmental and ecologic factors and their influence on the density of rodent populations are critical to understanding the epidemiology of this zoonosis. The epidemiology of HPS closely parallels the ecology of its rodent hosts. The majority of HPS patients have had clearly identifiable peridomestic, recreational, or occupational exposure to rodents of which the majority are the deer mouse (Peromyscus maniculatus), the primary rodent host for hantavirus and the most abundant rodent in North America. The most effective method to prevent infection with hantavirus is to avoid contact with any rodent species. Activities that should be avoided are using rodent inhabited buildings, cleaning barns or outbuildings infested with rodents, and disturbing rodent nests and burrows while hiking or camping.

When eliminating rodent infestation in homes or buildings, the following steps should be taken:

Keep mice and other rodents out of your house

  • Seal all openings into your home that are greater than 1/4 inch.

  • Keep all weeds, woodpiles, and garbage at least 100 feet from your home.

  • Keep all food, including pet food, in rodent proof containers.

  • Keep kitchens and food preparation areas clean.

Trap all mice within your home

  • Remember to wear gloves while handling mice.

  • Use snap traps to trap and kill mice.

  • Spray mice and trap with disinfectant.

  • Place rodent in a double plastic bag for disposal.

  • Leave several baited spring loaded traps inside the house at all times.

Clean up after mice

  • Wear rubber gloves while cleaning.

  • Air out area for 30 minutes.

  • Do not create dust by sweeping or vacuuming.

  • Spray rodent droppings and nests with disinfectant.

  • Place rodent droppings, nests, and other contaminated items in double bag for disposal.

  • Wash gloved hands in a general household disinfectant and then in soap and water.

  • Wash bare hands after removing gloves.

Figure 1. Hantavirus Pulmonary Syndrome Cases by County of Residence, Utah- May 2002

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Tuberculosis Testing at the Emergency Winter Shelter

The Utah Department of Health, Tuberculosis/Refugee Health Program, recently completed a Tuberculosis (TB) surveillance project at the Community Winter Emergency Housing Facility in Midvale. The TB surveillance project involved placing and reading tuberculin skin tests (TSTs) on persons seeking shelter at the facility in Midvale. TSTs are given to identify clients who have been infected with Mycobacterium tuberculosis. The TB Control/Refugee Health Program coordinated the program with the Road Home, formerly known as Traveler’s Aid Society, and the Fourth Street Clinic to ensure as many people as possible from this high risk population would be tested and treated if necessary. This project was started in November 1998 and has operated each year since, from early November to the last day that the shelter is open for the winter season (typically around April 1). During the winter season, each new client receives a TST as part of a targeted testing project used to protect the health of all the shelter clients. Testing began last year on November 5, 2001 and ended on March 27, 2002. A total of 375 people had a TST placed but 120 people did not return to have their TST read. Of the 255 clients who were both tested and read, 24 (9%) had a positive reaction (interpreted as a TST reaction of greater than or equal to 10 millimeters induration) and 231 (91%) had negative reactions. In comparison with the previous year’s targeted testing at the facility, 12% (28 out of 230) had a positive reaction.

Every week during the winter season, TB Control/Refugee Health Program staff and University of Utah medical students have placed TSTs on Monday and Tuesday nights, and read the results on Wednesday and Thursday nights. All clients who have a positive TST have been referred to the Fourth Street Clinic for further evaluation. Two major problems facing the Emergency Winter Shelter Testing Program are getting clients to return 48-72 hours after having a TST placed to get their TST result read, and getting clients with positive TSTs to go to the Fourth Street Clinic for further evaluation. Incentives, or small rewards (i.e., candy, sweatshirts, or socks), are given to those clients who do return for a test reading or clinic follow-up in an attempt to address these problems. It is anticipated, however, that getting clients to return for appropriate follow-up will be an ongoing problem. Most homeless people live under extreme circumstances and may have other problems such as substance abuse that make it difficult for them to comply with follow-up instructions.

The objectives of this project are to identify persons with latent TB infection or active TB disease, and to refer them for appropriate follow-up. It is hoped that, by addressing these objectives, the TB Control/Refugee Health Program and its partners will be able to reduce the overall incidence of TB in this high-risk population.

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Utah Department of Health, Office of Epidemiology
Monthly Morbidity Summary - May 2002 - Provisional Data

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The Epidemiology Newsletter is published monthly by the Utah Department of Health, Division of Epidemiology and Laboratory Services, Office of Epidemiology, to disseminate epidemiologic information to the health care professional and the general public.

Send comments to:
The Office of Epidemiology, Box 142104, Salt Lake City, UT 84114-2104 or call (801) 538-6191

Approval 8000008: Appropriation 3705

Rod Betit, Executive Director, Utah Department of Health
Charles Brokopp, Dr.P.H., Director, Division of Epidemiology and Laboratory Services
Gerrie Dowdle, MSPH, Manager, Surveillance and Disease Control Program, Managing Editor
Connie Dean, Community Health Technician, Surveillance and Disease Control Program, Production Assistant