in this study of human infections by snv in boulder county , colorado , we identified 2 patients who had trapped rodents for ecologic studies . on june 14 , 2005 ,
a 24-year - old man was admitted to boulder community hospital with fatigue , headache , fever , and thrombocytopenia ( 70,000 platelets/l ) but without cardiorespiratory compromise . a strip immunoblot assay identified immunoglobulin ( ig ) m and igg against snv n and gn proteins . on july 6 , 2005
, a 22-year - old igm- and igg - seropositive woman was admitted to boulder community hospital with fever and dyspnea ; she subsequently experienced bilateral lung infiltrates and thrombocytopenia ( 116,000 platelets/l ) .
she reported performing fieldwork in the same period as did patient 1 but with no overlap among the sites ( the distances between sampling sites where the 2 field workers most probably contracted their infections ranged from 6.4 to 9.8 km ) .
both patients engaged in field activities involving manipulating traps and rodents in areas where deer mice were seropositive for snv ( table ) .
* snv , sin nombre virus . along with the 2 patients , another 15 field workers were surveyed to assess possible exposures to snv .
ninety - five questions were asked involving , among others , contacts with rodents and use of personal protective measures and equipment .
most ( 83.3% , 14/15 ) reported previous experience with rodents in the field ; all workers were required to wear nitrile gloves and use a powered air - purifying respirator when handling animals .
no differences in risk exposure to contract hantavirus were evident between infected and noninfected persons .
six persons reported having been bitten > 1 times by rodents , including both case - patients .
patient 2 was bitten twice , with 1 bite resulting in bleeding despite the worker s use of nitrile gloves .
patient 1 reported being bitten by a vole ( microtus sp . ) on june 2 , and patient 2 was bitten by 2 deer mice on june 14 .
we hypothesized that the workers might have been exposed to a subset of rodents with unusually high titers of snv .
therefore , we resampled sites in boulder and jefferson counties in colorado ( where the field workers were infected ) during august 
a total of 44 sites were sampled during both trapping periods by using live traps ( h.b .
sherman traps , tallahassee , fl , usa ) in grids for 4 consecutive nights .
prairie dogs ( cynomys ludovicianus ) were also trapped at a subset of these study sites during june 
july 2005 with live traps ( tomahawk live traps , tomahawk , wi , usa ) .
a total of 1,868 animals from 10 mammalian species were captured during both trapping periods ( table ) .
we screened blood samples by strip immunoblot assay for antibodies against snv n protein ( 4 ) .
deer mice showed the highest abundance of seropositive samples , although harvest mice ( reithrodontomys megalotis ) , which carry el moro canyon virus , had higher seroprevalence .
two ( 2.5% ) of 81 hispid pocket mice ( chaetodipus hispidus ) were also positive but are unlikely to play an epidemiologic role .
small mammal capture frequencies varied during the 2 sampling periods ; seroprevalence for pocket mice , prairie voles , and harvest mice increased , and that for meadow voles ( m. pennsylanicus ) decreased .
we performed taqman ( applied biosystems , foster city , ca , usa ) quantitative real - time pcr on a subset of 79 ( of 187 ) samples from deer mice that had detectable antibodies to snv n antigen .
the samples selected for pcr analysis were those for which the volume of blood was deemed sufficient ( > 25 l ) to carry out a satisfactory rna extraction .
we chose 25 l as the minimal amount for detecting snv small segment rna by nested reverse transcription  pcr on the basis of a spiking experiment in which 5 l of lung homogenate from an infected deer mouse had been added to 20 l of blood from an uninfected deer mouse , resulting in a positive finding .
the equivalents of 10-l aliquots of total blood rna ( rneasy mini kit ; qiagen , valencia , ca , usa ) were subjected to quantitative real - time pcr with primers , probes , and pcr conditions as described ( 5 ) .
we detected only low levels of snv in the blood of 2 of the 79 seropositive deer mice tested ( table ) .
this low number of samples with detectable snv rna ( 2.53% ) is congruent with previous findings reporting undetectable levels of snv rna in blood using quantitative real - time pcr ( 6 ) .
the primary mode of hantavirus transmission to humans is through rodent excreta and secretions through the aerosol route ( 7 ) .
although indoor exposure in poorly ventilated buildings has been reported as a major factor for contraction of hcps , our survey supports the possibility that the 2 patients contracted snv outdoors and that , in at least in 1 case , a rodent bite was the proximate vehicle for transmission of snv to the field worker .
the fact that patient 1 was bitten by a vole and not by a deer mouse does not necessarily exclude transmission of snv by that route .
voles are not known to transmit snv , but there have been repeated instances of vole - associated hantaviruses being carried by sigmodontine rodents ( 11 ) .
although the power of this survey is limited by small sample size , we believe that our finding are potentially useful and suggest that increased attention be devoted toward avoiding rodent bites among the handlers of wild rodents in regions where hantaviruses occur .
although both workers sustained rodent bites , 1 by a known snv carrier and 1 by another rodent species , one should remain open - minded about the actual route of infection , which might still be through an airborne route rather than through bites in either case .
our results suggest that detecting snv rna of sufficient magnitude ( > 80 copies / ml ) to score as positive in taqman assays might be uncommon in the natural reservoir .
therefore , high loads of snv rna might not be a major factor in virus transmission in the wild .
alternatively , snv might cause only a brief rna viremia in wild deer mice ( 12 ) , and possibly the small number of real - time pcr  positive deer mice represents those animals that underwent recent seroconversion .
this phenomenon has also been observed with other rodent borne - hantaviruses ( 13 ) .
alternatively , or in addition , the small number of mice found to have quantifiable viral rna in this study might be a consequence of physiologic events ( such as viral recrudescence ) ( 14 ) , which result in intermittent detection of viral rna in blood , a phenomenon that might be shared by other agents of hemorrhagic fevers ( 15 ) .
 we report 2 cases of sin nombre virus ( snv ) infection in field workers , possibly contracted through rodent bites . 
 screening for antibodies to snv in rodents trapped in 2 seasons showed that 9.77% were seropositive . 
 quantitative real - time pcr showed that 2 of 79 deer mice had detectable titers of snv rna . 
The Study
Conclusions