METHODS: Rat facilities (i.e. rattery breeders or pet homes) were considered confirmed if recent human or rat SVI was identified and suspect if rats were received from/sent to confirmed facilities. We conducted trace-out investigations of rat movements from confirmed facilities to identify additional suspect facilities. In confirmed and suspected facilities, we obtained blood samples from human contacts and a sample of rats, and analyzed them using RT-PCR and ELISA serology. Characteristics of confirmed and negative facilities were compared using odds ratios.
RESULTS: As of March 23, 2017, 45 suspected Illinois facilities (13 ratteries and 32 pet homes) were identified; of those, 54% (n=7) of ratteries and 19% (n=6) of pet homes were confirmed. Trace-out investigations from these facilities identified over 70 suspected facilities in 13 states and Canada. Nine (12.9%) human samples and 115 (32.4%) rat samples were positive for SVI. Only 1 Illinois patient was hospitalized; the remainder were asymptomatic and none developed HFRS. Attack rates in confirmed ratteries were 100% (8/8) for human SVI and 40.1% (105/262) for rat SVI; in pet homes, attack rates were 7% (1/14) for human SVI and 10.8% (10/93) for rat SVI. Human and rat SVI rates were significantly higher in ratteries than in pet homes (χ2=26.9, p<0.001). The odds of being a confirmed facility were higher for ratteries than pet homes (OR = 5.5; 95% CI 1.2-26.0).
CONCLUSIONS: This investigation is the first to document SVI among pet rat owners in the United States. To date, the source of this outbreak remains unknown. The frequent trade and sale of rats led to widespread SVI throughout Illinois, making outbreak control challenging. Higher infection rates among ratteries might indicate elevated risk in that environment. Pet rat breeders should be aware of the risks of Seoul virus infection and take appropriate control measures including rat testing and proper hand hygiene.