In 1995, Salmonella Enteritidis (SE) cases in the state of Utah increased fivefold. Isolates were
identified as phage type 4 (PT4). Risk factors and sources of infection were investigated in two
case-control studies, a traceback of implicated foods, and environmental testing. Forty-three
patients with sporadic infections and 86 controls were included in a case-control study 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 study, restaurant dining was associated with illness (P = 0·002). In the
follow-up case-control study, case restaurants were likelier to use > 2000 eggs per week
(P < 0·02), to pool eggs (P < 0·05), and to use eggs from cooperative ‘A’ (P < 0·009). Eggs
implicated in separately investigated SE PT4 outbreaks were traced to cooperative ‘A’, and SE
PT4 was cultured from one of the cooperative's five local farms. We conclude that SE PT4
transmitted by infected eggs from a single farm caused a fivefold increase in human infections
in Utah.