The pandemic of Salmonella Enteritidis phage type 4 reaches Utah: a complex investigation confirms the need for continuing rigorous control measures

In 1995, Salmonella Enteritidis (SE) cases in the state of Utah increased f ivefold. Isolates were identified as phage type 4 (PT4). Risk factors and s ources of infection were investigated in two case-control studies, a traceb ack of implicated foods, and environmental testing. Forty-three patients wi th sporadic infections and 86 controls were included in a case-control stud y of risk factors for infection. A follow-up case-control study of 25 case and 19 control restaurants patronized by case and control patients examined risks associated with restaurant practices. In the first case-control stud y, restaurant dining was associated with illness (P = 0.002). In the follow -up case-control study, case restaurants were likelier to use > 2000 eggs p er week (P < 0.02), to pool eggs (P < 0.05), and to use eggs from cooperati ve 'A' (P < 0.009). Eggs implicated in separately investigated SE PT4 outbr eaks were traced to cooperative 'A', and SE PT4 was cultured from one of th e cooperative's five local farms. We conclude that SE PT4 transmitted by in fected eggs from a single farm caused a fivefold increase in human infectio ns in Utah.