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Hantavirus Pulmonary Syndrome -- Colorado and New Mexico, 1998

Hantavirus pulmonary syndrome (HPS) is a severe cardiopulmonary illness resulting in death in approximately 45% of cases. The most frequently recognized etiologic agent of HPS in North America, Sin Nombre virus (SNV), is transmitted to humans from its primary rodent reservoir, Peromyscus maniculatus (deer mouse), by direct contact with infected rodents, rodent droppings, or nests or through inhalation of aerosolized virus particles from mouse urine and feces. Sporadic cases occur throughout the United States and Canada, but the potential for spread from rodents to humans in 1998 probably has increased because of increased rodent population densities in some regions of the country. This report describes three cases of HPS that occurred in the southwestern United States with onsets of illness during April 15-28, 1998, and recommends methods to avoid exposure to rodents inside and around human dwellings.

Patient 1

On April 15, a 17-year-old man in Teller County, Colorado, developed fever (103.1 F {39.5 C}), headache, myalgia, and lower back pain. By April 17, he was somnolent and complained of a nonproductive cough and progressive shortness of breath. On medical examination he was hypotensive and dyspneic and was admitted to a hospital in respiratory distress. Bilateral infiltrates consistent with pulmonary edema were observed on his chest radiograph. Complete blood count (CBC) showed decreased platelets (32,000/mm3 {normal: 150,000/mm3-450,000/mm3}); a white blood cell count (WBC) of 19,600/mm3 (normal: 3200/mm3-9800/mm3), and a hematocrit (Hct) of 65% (normal: 39%-49%). He was intubated within 3 hours of admission, and serous fluid subsequently poured out of the endotracheal tube. The patient suffered a cardiac arrest on April 18 and could not be revived. Serologic studies conducted at the Colorado Department of Public Health and Environment's virology laboratory were positive for anti-SNV IgM antibodies (1).

The patient lived with his family on a sheep ranch with open pastures surrounded by Ponderosa pine forest. The patient spent a large amount of time in a converted garage used as a studio where he often slept on a rodent-infested couch. Evidence of rodent infestation was observed in the numerous buildings, barns, and unused vehicles on the property.

Patient 2

On April 25, a 23-year-old man residing in San Juan County, New Mexico, sought care at a local emergency department (ED) for midsternal chest pain, difficulty breathing, sore throat, generalized aches and pains, nausea, vomiting, and fever of 5 days' duration. Examination revealed an oral temperature of 101.7 F (38.7 C) and an injected oropharynx. A CBC showed decreased platelets (111,000/ mm3); WBC of 4200/mm3; and Hct of 44.7%. A chest radiograph was normal. Bronchitis was diagnosed, and the patient was discharged. On April 27, the patient sought care at a different ED for sore throat, chest pain, nausea, and vomiting. He reported increasing abdominal pain with cramping and diarrhea. He appeared dehydrated, and his temperature was 100.8 F (38.2 C). The chest was clear to auscultation. Platelets were measured at 51,000/mm3; WBC, 8100/mm3; and liver enzymes were mildly elevated. Hepatitis was suspected. The patient was administered intravenous fluids and an antiemetic before being discharged. On April 28, he returned complaining of blurry vision, dizziness when standing, increased diarrhea, and bilateral thigh cramping and pain. Clinical evaluation at that time revealed acute respiratory distress with decreased platelets (14,000/mm3) and increased Hct (58.9%). HPS was tentatively diagnosed. The patient's status declined rapidly and he died shortly after arriving at a regional medical facility. The diagnosis of acute SNV infection was confirmed using a strip immunoblot assay performed at the University of New Mexico (2).

Examination of the homesite revealed approximately 10 unused vehicles on which the patient worked frequently; all had evidence of rodent infestation. The patient slept on the floor of a mobile home in which droppings were found beneath the kitchen sink. The patient worked for a construction company and, according to his family, did jobs that included crawling under mobile homes to dig holes and pour pilings. Co-workers did not report any obvious exposures to rodents or rodent-infested areas.

Patient 3

On April 29, a 29-year-old woman residing in McKinley County, New Mexico, reported fever, myalgia, decreased appetite, headache, vomiting, back pain, and chills, and a seasonal, allergy-related cough. When examined at a local ED, her temperature was 101.5 F (38.6 C). A viral infection was diagnosed, and she was sent home. On May 1, she went to a different facility with worsening symptoms, including ear pain, nausea, and a dry cough that had worsened. A CBC showed thrombocytopenia, and she was transferred to the first facility's ED. Blood tests revealed a platelet count of 66,000/mm3; WBC, 4700/mm3; and Hct, 47.0% (normal: 33%-43%). HPS was tentatively diagnosed, and the patient was immediately transferred to a regional medical facility. Chest radiographs were clear on the evening of admission and the following morning, but by the evening of May 2 her cough had continued to worsen and bilateral infiltrates were observed on her radiograph. On May 3, peak lactate was 5.5 mmol/L (normal: 0.5-2.0 mmol/L), and the cardiac index was 1.9. The patient improved with dobutamine and supplemental oxygen and was discharged in stable condition on May 9. A strip immunoblot assay was positive on a serum sample taken approximately 24 hours before the appearance of pulmonary infiltrates (2).

The patient lived with her parents on a ranch. Rodents were seen occasionally outside of the house, and a mouse carcass was found in the house 2 weeks before the patient's onset of illness. An on-site investigation revealed rodent droppings in several closets in the house, including the patient's.

Rodent Monitoring

Since 1994, rodent populations have been continuously monitored at selected sites in Arizona, Colorado, and New Mexico. Estimated rodent population densities have increased at most trapping sites 10-20-fold from March 1997 to March 1998 (T. Yates, Ph.D., University of New Mexico, personal communication, 1998).

Reported by: D Keller, MD, P Ettestad, DVM, CM Sewell, DrPh, State Epidemiologist, New Mexico Dept of Health. R Rains, MD, Memorial Hospital, S Englender, MD, El Paso County Health Dept, Colorado Springs; T Woods, ScD, Teller County Health Dept, Woodland Park; J Pape, D Tanda, J Reynolds, R Hoffman, MD, State Epidemiologist, Colorado Dept of Public Health and Environment. G Mertz, MD, G Scully, MD, D Mapel, MD, F Koster, MD, J DeLury, MD, C Hansbarger, Dept of Internal Medicine, B Hjelle, MD, Pathology Dept, T Yates, PhD, Dept of Biology, Univ of New Mexico, Albuquerque. J Iralu, MD, C Freeman, MPH, B Hroch, A Nunes, D Loretto, regional medical facility. D Peter, MD, R Fulgham, MSPH, L Courtois, M Mattson, MPH, R Charleston, Area Office, J Cheek, MD, Div of Community and Environmental Health, Indian Health Svc. State Br, Div of Applied Public Health Training (proposed), Epidemiology Program Office; Div of Quarantine, Special Pathogens Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; and an EIS Officer, CDC.

Editorial Note

Editorial Note: In addition to the three persons described in this report, a total of 183 confirmed cases of HPS from 29 states have been reported to CDC. More cases have occurred among males (61%) than among females, and the mean age of case-patients is 37 years (range: 11-69 years). HPS cases have occurred more often in rural areas that are associated with hantavirus-carrying rodents (CDC, unpublished data). Of all cases, 75% occurred among whites and 20% among American Indians; of these, 11% were of Hispanic ethnicity.

The distribution of the rodent hosts of the four different hantaviruses known to cause HPS in North America includes all the contiguous United States (3,4). In 1997, particularly in parts of the southwest, El Nino has been associated with increased winter rainfall, improving rodent food supplies and resulting in higher densities of rodents. Prolonged El Nino events preceded the first known HPS epidemic in 1993.

The most common early symptoms of HPS include fever; myalgia, particularly in large muscle groups of the lower back; nausea; vomiting; and diarrhea. However, distinguishing signs of HPS include fever and myalgia associated with thrombocytopenia, presence of immunoblasts, and hemoconcentration (5). HPS should be suspected in patients with these signs and symptoms, especially those who live in rural or semirural areas or who have had an identifiable rodent exposure. No specific antiviral therapy is available to treat HPS, although a double-blind, placebo-controlled trial is under way to evaluate the potential efficacy of ribavirin. * In a preliminary open label trial, no difference in case-fatality was identified. Early recognition of hantavirus infection and case management with careful hemodynamic monitoring, early use of inotropes, avoidance of overhydration, and supportive therapy may increase survival.

Although the specific site of exposure is unknown for the three persons described in this report, all lived on premises with substantial peridomestic rodent infestations. Limiting exposure to rodents and their excreta is the most effective means of decreasing the risk for HPS. Measures to decrease such exposures in and around a home or workplace include eliminating food sources available to rodents in structures used by humans, limiting possible nesting sites, sealing holes and other possible entrances for rodents, and using "snaptraps" and rodenticides (6). Other methods include using a 10% bleach solution to disinfect dead rodents and wearing rubber gloves before handling trapped or dead rodents; gloves and traps should be disinfected after use. Before entering areas that have potential rodent infestations, doors and windows should be opened to ventilate the enclosure. Persons entering these areas should avoid stirring up or breathing potentially contaminated dust. Dusty or dirty areas or articles should be moistened with a 10% bleach solution or other disinfectant solution before being cleaned -- brooms or vacuum cleaners should not be used to clean rodent-infested areas. Decreasing the number of rodents inside and around human dwellings remains the most effective means to prevent peridomestic hantavirus infection.

References

  1. Ksiazek TG, Peters CJ, Rollin PE, et al. Identification of a new North American hantavirus that causes acute pulmonary insufficiency. Am J Trop Med Hyg 1995;52:117-23.

  2. Hjelle B, Jenison S, Torrez-Martinez N, et al. Rapid and specific detection of Sin Nombre virus antibodies in patients with hantavirus pulmonary syndrome by a strip immunoblot assay suitable for field diagnosis. J Clin Microbiology 1997;35:600-8.

  3. Hall ER, Kelson KR. The mammals of North America. New York, New York: Ronald Press, 1959.

  4. Doyle T, Bryan R, Peters CJ. Viral hemorrhagic fevers and hantavirus infections in the Americas. Infect Dis Clin North Am 1998;12:95-110.

  5. Moolenaar RL, Dalton C, Lipman HB, et al. Clinical features that differentiate hantavirus pulmonary syndrome from three other acute respiratory illnesses. Clin Infect Dis 1995;21:643-9.

  6. Glass GE, Johnson JS, Hodenbach GA, et al. Experimental evaluation of rodent exclusion methods to reduce hantavirus transmission to humans in rural housing. Am J Trop Med 1997;56:359-64.

* Additional information on the trials is available from Dr. Greg Mertz, University of New Mexico School of Medicine, telephone (505) 272-5666, or Lanette Sherill, University of Alabama at Birmingham, telephone (205) 934-3411.


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