Foodborne Illness, Epidemiology, and Risk Assessment
Agents, onset, and investigation
Separate the mechanisms: intoxications (preformed toxin; Staphylococcus aureus, Bacillus cereus emetic type, Clostridium botulinum) produce symptoms quickly, often 1 to 6 hours; infections (Salmonella, Shigella, Campylobacter, Vibrio) typically take 12 hours to several days; toxin-mediated illnesses such as E. coli O157:H7 and Clostridium perfringens fall in between. Norovirus is famously rapid (12 to 48 hours) with high secondary attack rates.
Know the "Big 6" pathogens the Food Code singles out because of low infectious dose or severity: nontyphoidal Salmonella, Salmonella Typhi, Shigella, Shiga toxin-producing E. coli, hepatitis A, and norovirus. These drive exclusion, reporting, and no-bare-hand-contact rules.
Epidemiology questions favor definitions. An outbreak is two or more illnesses from a common exposure; an attack rate is ill divided by exposed. Investigations move from detection and confirmation through case finding, hypothesis generation (often a case-control or cohort study producing an odds ratio or relative risk), environmental and laboratory investigation, control measures, and follow-up. Risk assessment has four steps: hazard identification, hazard characterization (dose-response), exposure assessment, and risk characterization; risk management and communication follow.
Trap: choosing a pathogen by food vehicle alone rather than by incubation period and symptom pattern. Worked example: at a banquet, 45 of 180 attendees become ill 30 hours later with diarrhea, and 40 of 60 who ate the ham are ill versus 5 of 120 who did not. Ham attack rate is 67 percent, others 4 percent; the high relative risk plus a 30-hour onset points to a bacterial infection such as Clostridium perfringens rather than a preformed toxin.