Person-to-person transmission within a family is both common and exceedingly well-documented in the extant literature, including numerous cases in which the primarily infected person was asymptomatic. See, e.g. K. Ludwig, “Outbreak of Escherichia coli O157:H7 Infection in a Large Family,” Eur. J. Clin. Microb. Infect. Dis. Vol. 16, at 238-41 (1997); P. Rowe, “Diarrhea in Close Contacts as a Risk Factor for Childhood Hemolytic Uremic Syndrome,” Epidem. Infect. 110:9-16 (1993).
Secondary transmission cases are well understood in the scientific community to be an inevitable part of any foodborne illness outbreak. See E. Belongia, et al., “Transmission of Escherichia coli 0157:H7 Infection in Minnesota Child-Care Facilities,” JAMA, at 887 (Feb. 17, 1993) (describing the inevitable spread of illness from primary to secondary cases). Indeed, it is the inevitability of secondary transmission that drives a health department to find the source of outbreaks as quickly as possible; it is secondary cases that they are trying to minimize or prevent.
In fact, in the context of an outbreak of E. coli O157:H7, a Court has already held (in a case I tried), as a matter of law, that secondary infection is a foreseeable consequence of such an outbreak. See Almquist et al. v. Finley School Dist., 57 P. 3d 1191 (Wash. App. 2002) cert. denied 75 P.3d 968 (2003).