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Hantavirus Pulmonary Syndrome in Northern Alberta, Canada: Clinical and Laboratory Findings for 19 Cases Author(s): R. Verity, E. Prasad, K. Grimsrud, H. Artsob, M. Drebot, L. Miedzinski, J. Preikasaitis Source: Clinical Infectious Diseases, Vol. 31, No. 4 (Oct., 2000), pp. 942-946 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/4461342 Accessed: 31/08/2009 15:37 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. 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Preiksaitist'3 'Provincial Laboratory of Public Health for Northern Alberta, 2AlbertaHealth, and 3Departmentof Medicine, University of Alberta, Edmonton, Alberta, Canada; and 4CanadianScience Centrefor Human and Animal Health, Winnipeg, Manitoba, Canada We reviewed the clinical and laboratory findings for 19 cases of hantavirus pulmonary syndrome (HPS) identified either serologically or by immunohistochemical testing of archival tissue at our tertiary care center. Fever (95%), cough (89%), and dyspnea (89%)were the most common presenting symptoms. The most prevalent presenting signs were respiratory abnormalities (95%) and tachycardia (84%). Common laboratory findings included thrombocytopenia (95%) and leukocytosis (79%). Elevated aspartate aminotransferase and lactate dehydrogenase levels were found in all patients tested. Intubation was required in 58% of the patients, and inotropic support was required in 53%. Our study confirms that serological responses appear early during clinical illness, making the enzyme immunoassay a useful tool for the diagnosis of acute HPS. The mortality (26%)and severity of disease that we observed among patients with HPS appear to be less than those reported elsewhere. In fall of 1992, there was an exceptional amount of rainfall in the Four Corners region of the United States; this led to the growth of a massive deer mouse (Peromyscusmaniculatis) population during the following year [1]. In May 1993, an outbreak of a mysterious disease occurred in rural New Mexico [1]. A case definition was developed by the Centers for Disease Control and Prevention (CDC) [1]. The causative agent of this disease, a hantavirus identified by the CDC by means of serological testing, was designated as "Sin Nombre" ("No Name") virus, and the syndrome became known as hantavirus pulmonary syndrome (HPS) [1-9]. Transmission of Sin Nombre virus to humans in North America is believed to occur through exposure to deer mice or deer mice excreta [10, 11]. The mortality associated with this syndrome has been reported to be as high as 43% in the United States (as of May 1999) [12]. Before the outbreak in New Mexico occurred in 1993, there had been no reports of HPS in North America. Since the original outbreak of HPS occurred in the Four Corners region of the United States in 1993, there have been numerous reports of the disease throughout both North and South America [12-19]. In Canada, 20 cases have been reported in Alberta, 6 in British Columbia, 5 in Saskatchewan, and 1 in Manitoba (as of 1 September 1999). We observed (a) that the cases of HPS seen in northern AlReceived 1 October 1999;revised9 March2000; electronicallypublished 25 October 2000. Reprints or correspondence:Robert Verity, Microbiology and Public Health, 2B3.01 Walter C. Mackenzie Health Sciences Centre, University of Alberta Hospitals, 8440-112 St., Edmonton, Alberta T6G 2J2, Canada ([email protected]). ClinicalInfectiousDiseases 2000;31:942-6 ? 2000 by the InfectiousDiseasesSocietyof America.All rightsreserved. 1058-4838/2000/3104-0014$03.00 berta were associated with a mortality rate that was lower than that previously reported in the United States and (b) that the majority of cases in Canada have occurred in Alberta. This report describes the exposure history, symptoms, signs, treatment, outcome, and laboratory diagnosis of 19 cases of HPS that occurred in northern Alberta from 1989 through June 1998. Patients and Methods Patient population. During the period from September1994 through June 1998, 19 cases of HPS were identifiedat 3 tertiary care centers in Edmonton, Alberta, Canada. Three of these cases occurredin 1989, 1990, and 1992, respectively,and were identified retrospectivelywith the use of archivalblood and tissue samples. All cases of HPS were confirmedeither by positive serology or by immunohistochemicalstaining of archivaltissues. All cases fit the CDC case definition of HPS [1]. A chart review of the exposure history, symptoms, signs, treatment,and outcome was performed for all cases of HPS treated in Alberta, by use of a standardized database form. Diagnostic tests. Serum samples obtained from the patients were tested against Sin Nombre nucleocapsidantigenand a normal control antigen by use of an EIA, as describedelsewhere [8]. In February 1998, all but 3 of the patients' specimenswere tested at the Canadian Science Centre for Human and Animal Health, in Winnipeg,Manitoba, by use of an EIA on 1 standardizedtest run. Those patients whose serum specimenswere not included in this test run had HPS diagnosed after December 1997. The dilutions of human serum that were used were 1:100, 1:400, 1:1600, and 1: 6400. The cutoff point for a positive test was an optical density of 0.1 when comparedto background.The serumtiterwas determined to be the highest dilution at which a positive result was obtained. Formalin-fixedtissue specimensfrom 2 patients were tested by means of immunohistochemicalstaining (testing was done by Dr. S. Zaki, CDC, Atlanta) [8]. Blood clots and tissues from both a CID 2000;31 (October) HPS in Northern Alberta, Canada representativeseropositivedeermouse and a patientwith HPS were used for reverse transcriptase-PCRamplificationof a portion of the hantavirusG1 gene, with use of primersdescribedby Johnson et al. [20]. Statistical analysis. A 2-tailed nonparametric1-sample t test (a = .05), done with the use of SPSS software,version 9.0 (SPSS, Chicago), was performed to compare the number of days from onset of symptoms to presentationin the patients who survived and in those who died. andr-~~~~~~~~0 943 9 11998 1,~~~1997 ~~~~ 87~ 7 1 a 6-1 8~~~ ~~51 r1996 ? 0~1 ~1 0 1111995 01994 11992 1989 Zell/L) 23 Results The medical records of all 19 patients were available for this study. The median age of the patients was 40 years (range, 15-65 years). Eleven (58%) of the patients were men. The median time from onset of symptoms to presentation was 5 days (range, 2-19 days). The majority of cases of HPS occurred in the spring (figure 1). Ten (53%) of the 19 cases presented between 1 June 1997 and 19 June 1998. All of the patients were treated at our 3 tertiary care centers. Eighteen of the 19 patients were from rural Alberta, and 1 patient, who was working in Fort St. John, British Columbia, was from Saskatchewan (figure 2). All but one of the patients had a known exposure to mice or mice excreta in the 6 weeks prior to the onset of illness. The one patient who did not have an identified history of exposure to mice had a pet gerbil at home. A blood sample obtained from the gerbil was sent for serological testing and was found to be negative for evidence of hantavirus infection. Symptoms and signs. In a retrospective study, it is difficult to ascertain whether the physician who obtained the history asked about specific symptoms, since negative findings are sometimes not recorded. We assume that a search for the symptoms listed below was done for all critically ill patients. The most common symptoms at the time of presentation were fever (95%), cough (89%), and dyspnea (89%). In 7 (41%) of the 17 patients, the cough was nonproductive. Other frequently reported symptoms included nausea (74%), chills (63%), and vomiting (58%). Headache was reported by 12 patients (63%), of whom 4 had a lumbar puncture performed as part of their initial workup. The occurrence of rhinorrhea and sore throat, symptoms that may not have been consistently sought, was documented in only 2 patients. The most prevalent presenting signs were respiratory abnormalities (95%), tachypnea (84%), and tachycardia (84%). Hypotension at presentation, which was defined by a value of<100 mm Hg systolic pressure, was noted in only 32% of patients. Abnormalities on chest radiography were seen in 18 (95%) of 19 patients at the time of presentation. All of these patients had interstitial infiltrates, and 5 (28%) of 18 patients had pleural effusions. Laboratory values. Common hematological abnormalities that were seen during the clinical course of HPS included thrombocytopenia (95%) and leukocytosis (79%). The trough Sprng Summer Fall Winter Figure 1. Seasonalityof cases of hantaviruspulmonarysyndrome (HPS)in northernAlberta,Canada(as of December1998).Eachpatternrepresentsa yearin whichat leastone caseof HPSwas diagnosed. medianplateletcount was 52 x 109cells/L(range,193-9 x 109 cells/L),and the peakmedianWBCcount was 18.5x 109cells/ L (range, 5.7-59.2 x 109cells/L). Increasedhemoglobinand hemoconcentration were seen in 5 (26%) of the 19 patients. The partial thromboplastin time was increased in 16 (89%) of 18 patients. Five (45%) of the 11 patients who had a peripheral blood smear prepared, with or without bone marrow aspiration, had atypical lymphocytes seen by a hematopathologist. The other laboratory abnormalities included elevated levels of aspartate aminotransferase in 17 patients and elevated levels of lactate dehydrogenase in 15 patients. The peak median value was 124 IU/L (range, 57-23,120 IU/L) for aspartate aminotransferase and 657 IU/L (range, 279-20,200 IU/L) for lactate dehydrogenase. Thirteen (93%) of 14 patients had hypoalbuminemia. An increased creatinine kinase concentration was seen in 6 (43%) of 14 patients. The creatinine level was elevated in 58% of patients. For 6 patients, the median arterial partial pressure of 02 on room air at the time of admission was 46.5 mm Hg (range, 39-51 mm Hg). All of the patients required supplemental oxygen at the time of admission. The plasma lactate level was elevated in 5 (50%) of 10 patients, and the venous bicarbonate level was low in 15 (79%) of 19 patients during the hospital days prior to and during the first week in the intensive care unit. The peak median level of plasma lactate was 2.7 mM/L (range, 1.0-20.4 mM/L), and the trough median level for venous bicarbonate was 18 mM/L (range, 8.2-25 mM/L) during this time. Clinical outcome. Five (26%) of the 19 patients died. One (33%) of the 3 patients who had HPS diagnosed retrospectively before 1994 and 4 (25%) of the 16 patients who had HPS diagnosed after 1994 did not survive. For the 10 cases diagnosed from 1997 through 1998, the mortality rate was 30%. The median time from the onset of symptoms to presentation was 6.5 days (range, 2-19 days) for the patients who survived 944 Verityet al. and 3 days (range, 2-6 days) for those who died. With regard to the time from onset of symptoms to presentation, there was no significant difference between the survivors and those who died. Intubation was required for 11 (58%) of 19 patients. For those patients who survived, the median time from onset of symptoms to intubation was 6.5 days (range, 4-21 days); for those who died, it was 4 days (range, 2-6 days). The median duration of intubation was 6 days (range, 2-70 days) for those who survived and 1 day (range, 1-4 days) for those who died. Ten (71%) of the 14 patients who survived had a mean arterial pressure (MAP) of <70 mm Hg recorded during the clinical course of HPS, and 5 (50%) of these 10 patients required inotropic support. All patients who died had a MAP of <70 mm Hg during the clinical course of HPS and required inotropic support. The median duration of hospitalization was 9 days (range, 6-85 days) for those who survived, and for those who died, the median interval from presentation to death was 2 days (range, 1-5 days). Two (14%) of the 14 surviving patients were treated with ribavirin, and 5 patients (26%) were enrolled in a randomized clinical trial of ribavirin versus placebo. Diagnostic testing. Blood samples for serological testing were collected from all of the patients (table 1). A positive IgM response was seen in 17 (89%) of 19 patients at the time of the first serological testing, at a median of 7 days (range, 2-21 days) after the onset of symptoms. One of the patients who was initially seronegative had a positive IgM response when retested 14 days after the onset of symptoms, and the other (for whom CID 2000;31 (October) Table 1. Results of serological testing of blood samples obtained from 19 patients with hantavirus pulmonary syndrome (HPS). Reciprocal titer for 1st Reciprocal titer for 2d Reciprocal titer for 3d specimen specimen specimen Patient IgM IgG Daya 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 1600 100 6400 400 100 400 <100 1600 1600 1600 100 400 <100 1600 6400 100 1600 400 1600 100 <100 100 400 <100 400 <100 <100 100 100 <100 <100 <100 100 100 <100 1600 400 <100 2 4 4 4 4 5 6 6 7 7 7 7 IgM IgG Daya IgM IgG Daya 400 400 1600 100 8 16 <100 <100 1600 400 37 361 400 <100 14 400 400 31 1600 400 21 1600 400 22 <100 400 1600 400 149 27 <100 400 62 400 100 34 <100 400 1545 7b 8 9 10 18 21 21 a Number of days from onset of symptoms to serology. b HPSwasdiagnosedin thispatientby meansof immunohistochemical staining of archivaltissues.A blood samplehad been collectedfromthis patientin 1989, which may account for the lack of IgM reactivity. no further serological results were available) had the diagnosis confirmed by immunohistochemical staining of tissue. Blood samples from this patient had been collected in 1989. The long period of storage may account for the lack of IgM reactivity. Alberta ? Edmonton * Calgary Figure 2. Geographic locations of cases of hantavirus pulmonary syndrome (HPS) in northern Alberta, Canada. One patient, who was referred to our tertiary care center from Fort St. John, British Columbia, was a resident of Saskatchewan. Squares, cities; circles, cases of HPS. CID 2000;31 (October) The IgM responsewas positivein 14 (88%)of 16 patientswho had theirblood collectedwithin 10 days of the onset of symptoms, and it lasted as long as 34 days in 1 patient.After this point, the IgM responsebegins to decline.In 10 (53%)of 19 patients,an IgM and IgG responsewas seen duringthe first serologicaltest. Duringsubsequenttesting,whichwas done at a median of 25 days (range, 16-31 days) after the onset of symptoms,a further4 (44%)of 9 patientshad a Sin Nombre-specificIgG responsedetected.Four years after development of acute HPS, 1 patienthad an IgG titer of 1:400to Sin Nombrevirus. Sequence analysis of hantavirusG1 ampliconsgenerated from both a patientwith HPS (patient8; table 1) and a seropositivedeermousefromnorthernAlbertaseemsto show that thesehantavirusesweregenotypicallyrelatedto eachother(figure 3). Althoughgenotypicallydistinctfrom Sin Nombreand Convict Creek 107 strains,the northernAlbertahantaviruses appearto be morecloselyrelatedto thesestrainsthanto eastern North Americanhantaviruses,such as the New Yorkor Black CreekCanalviruses(figure3). Discussion 945 HPS in Northern Alberta, Canada Ab-rodent Ab-human CC107 SN -~- NY BCC PH TUL PUU HTN SEO Figure 3. Phylogenetic relationship of northern Alberta (Ab) Sin Nombre-like viral strains to other hantaviruses, according to the nucleotide sequence from the G1 gene. This tree was generated with the use of Clustal V (included in the Lasergene Megalign program;DNASTAR, Madison, WI) [21]. Definitions of strains and GenBank accession numbers (given in parentheses) for the sequence are as follows: CC107, Convict Creek 107 (L33474); SN, Sin Nombre virus strain (NMH10 and L25783); NY, New York-1 (U36802); BCC, Black Creek Canal virus (L39950); PH, Prospect Hill (X55129); TUL, Tula/Moravia/5286/ 94 strain (Z66538); PUU, Puumala, Sotkama strain (X61034); HTN, Hantaan virus (M14627); and SEO, Seoul virus strain KI-83-262 (D17592). which was noted in 32%of patients,comparedwith 50%of patientsin an earlierstudy[4].Only 2 patientshad rhinorrhea and a sorethroat,a findingdemonstratingthatthesesymptoms are usefulin differentiatingHPS fromdiseasecausedby influenza [22]. In contrastto a previousstudy of symptomsseen withHPS,manypatientsin our serieshadcoughas a presenting symptom,suggestingthat lack of cough was not usefulin differentiatingHPS from other causesof pneumonia[23]. The laboratoryresultsseen in this seriesof cases are similar During the period from June 1997 throughJune 1998, 10 cases of HPS were diagnosedat our centers;this is a greater numberof casesthanwas reportedin the areaduringtheperiod from 1989 through1996.As previouslydiscussedwith regard to the Four Cornersoutbreak,El Nifio weathereffectsseemed to boost the deer mouse population[1]. A similarpopulation explosionmay have occurredamongdeermicein Albertadurto those reported elsewhere, with thrombocytopenia, leukocying the summerof 1997, resultingin increasedexposureof humansto mice. In 1997,most of the cases of HPS occurred tosis with a left shift, and an increasein lactatedehydrogenase duringthe fall, when the mice may have been seekingshelter level being common [1-9]. However,the patientsin our study indoors. did not have the same incidenceof hemoconcentration, which The age rangeof the patientsvariedwidelyin our study,with is anothermarkerof severedisease.A recentstudyalso showed the youngestpatientbeing 15 yearsold. This is similarto findthatthefindingby hematopathologists of an increasein atypical from in studies the United 4 States,where,as of February lymphocytesin peripheralblood smearsis useful for the diings 2000, there have been no confirmedcases involvingchildren agnosis of HPS; this observationwas made for 45% of our level aged <10 years age (www.cdc.gov/ncidod/diseases/hanta/hps/patients[1]. In this study,the aspartateaminotransferase was elevatedin 100%of the patients,a findingthat suggests noframes/caseinfo.htm). Why childrendo not contractthe illthat a normalresultmakes a diagnosisof HPS far less likely. ness, however,is not entirelyunderstood.One hypothesisis that HPS is immunopathologicalin natureand that repeated A study of the first 100 cases found in the United States showed that 65 (84%)of 77 patients requiredintubation,a exposureto Sin Nombrevirusis requiredto cause disease. Analysisof the geographiclocationsof the cases of HPS on proportionthat is higherthan the 11 (58%)of 19 patientswho a map of Albertarevealsthat they fit into a belt-likepattern requiredintubationin our study [5]. When hypotensionwas in the midregionof the province(figure2). Recentstudieshave recordedduring the clinicalcourse of HPS, 79%of patients had a MAP of u70 mm Hg, and 53% required inotropic supsuggestedthat multipleenvironmentalfactorsmay play a part in the increasein the numberof deer mice and in subsequent port. Data on hypotensionduringthe clinicalcourse of HPS increasesin the numberof cases of HPS [22]. Most of the have not been given in previousstudy reports. in our involved the inhalation of aerosols from Our study confirmsthat serologicalresponsesappearearly exposures study areascontaminatedwith mouse excreta. duringclinical illness, making the EIA a useful tool for the The symptomsand signs observedat presentationin this diagnosisof acuteHPS. The IgM serologyfor 1 of the patients are similar to those for a lower was study reportedpreviously,except negativeon day 6 of the illness but becamepositive on incidenceof markersof severe disease, such as hypotension, day 14; this findingemphasizesthat if there is a clinicalsus- 946 Verityet al. picion of HPS, serological testing should be repeated. The IgG antibodies to Sin Nombre virus seem to persist for a long time, as was illustrated by the patient who had an IgG titer of 1:400 4 years after acute HPS developed. A recent study indicated that the Sin Nombre-like viruses found in Alberta deer mice were genotypically distinct from the Sin Nombre virus strains in the southwestern United States [24]. However, this study also showed that western North American Sin Nombre-like viruses seemed, at the genotypic level, to be more related to each other than to strains found in eastern regions of the continent. Our findings are consistent with this observation. Northern Alberta viral strains both from a patient with HPS and a seropositive deer mouse also showed a closer genetic relationship to western Sin Nombre viruses than to such viruses as the New York or Black Creek Canal viruses. In our series, we observed a lower incidence of signs of severe disease at admission, a lower incidence of intubation, and a lower mortality (26%) than those observed by other investigators. The case-fatality rate of 25% seen since 1994 in our series of patients can be compared with the case-fatality rate of 34% reported from the United States since 1994 (as of 4 February 2000); however, because of the small number of patients in our study, this difference may not be significant (www .cdc.gov/ncidod/diseases/hanta/hps/noframes/caseinfo.htm). The low case-fatality rate observed may be the result of earlier detection of infection, aggressive intensive care unit management, the viral inoculum to which the patients were exposed, the genetic predisposition of the patients, or the presence of a variant of the virus in northern Alberta. Further genetic analyses of Sin Nombre isolates from our region and from other regions would be useful for differentiating between these possibilities. Acknowledgments 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 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