Hantavirus:  An Introduction

Small But Deadly
Hantavirus Pulmonary Syndrome (HPS) has been recognized as a disease only recently in North America. So far, it's also fairly uncommon and the chances of becoming infected are low. However, HPS is potentially deadly and immediate intensive care is essential once symptoms appear.

The Mouse That Roared
Hantaviruses that cause HPS are carried by rodents, especially the deer mouse. You can become infected by exposure to their droppings, and the flu-like first signs of sickness (especially fever and muscle aches) appear one to six weeks later, followed by shortness of breath and coughing.  Once this phase begins, the disease progresses rapidly, necessitating hospitalization and often ventilation within 24 hours.

Prevention is the best strategy, and it simply means taking some very practical steps to minimize your contact with rodents. HPS is not contagious from person-to-person in the United States

Clinical Case Definition
An illness characterized by one or more of the following clinical features:

	A febrile illness (i.e., temperature >101°F [38.30°C]) occurring in a previously healthy person characterized by a) unexplained Adult Respiratory Distress Syndrome (ARDS) or b) bilateral interstitial pulmonary infiltrates with respiratory compromise requiring supplemental oxygen, developing within 72 hours of hospitalization.
	An unexplained respiratory illness resulting in death, with an autopsy examination demonstrating non-cardiogenic pulmonary edema without an identifiable cause.
	Presentation and First Evaluation Patients with HPS typically present in a very nonspecific way with a relatively short febrile prodrome lasting 3-5 days. In addition to fever and myalgias, early symptoms include headache, chills, dizziness, non-productive cough, nausea, vomiting, and other gastrointestinal symptoms. Malaise, diarrhea, and lightheadedness are reported by approximately half of all patients, with less frequent reports of arthralgias, back pain, and abdominal pain. Patients may report shortness of breath, (respiratory rate usually 26 - 30 times per minute). Typical findings on initial presentation include fever, tachypnea and tachycardia. The physical examination is usually otherwise normal. HPS Clinical Presentation Most Frequent Frequent Other fever headaches shortness of breath chills nausea, vomiting dizziness myalgias abdominal pain arthralgia   diarrhea back or chest pain   cough sweats   malaise   The diagnosis is seldom made at this stage, as cough and tachypnea generally do not develop until approximately day seven. Once the cardiopulmonary phase begins, however, the disease progresses rapidly, necessitating hospitalization and often ventilation within 24 hours. Signs that make a diagnosis of HPS unlikely include rashes, conjunctival or other hemorrhages, throat or conjunctival erythema, petechiae, and peripheral or periorbital edema.

Laboratory Criteria for Diagnosis

	Detection of hantavirus-specific immunoglobulin M or rising titers of hantavirus-specific immunoglobulin G, or
	Detection of hantavirus-specific ribonucleic acid sequence by polymerase chain reaction in clinical specimens, or
	Detection of hantavirus antigen by immunohistochemistry

Surveillance Case Classification
Confirmed: A clinically-compatible case with laboratory criteria for diagnosis

Comment
Laboratory testing must be performed or confirmed at a reference laboratory. Because the clinical illness is non-specific and ARDS is common, a screening case definition should be used to determine which patients to test. In general, a predisposing medical condition (e.g., chronic pulmonary disease, malignancy, trauma, burn, and surgery) is a more likely cause of ARDS than hantavirus, and patients who have these underlying conditions and ARDS should not be tested for hantavirus.

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