Outbreak characteristics associated with identification of contributing factors to foodborne illness outbreaks.

Information on the factors that cause or amplify foodborne illness outbreaks (contributing factors), such as ill workers or cross-contamination of food by workers, is critical to outbreak prevention. However, only about half of foodborne illness outbreaks reported to the United States' Centers for Disease Control and Prevention (CDC) have an identified contributing factor, and data on outbreak characteristics that promote contributing factor identification are limited. To address these gaps, we analyzed data from 297 single-setting outbreaks reported to CDC's new outbreak surveillance system, which collects data from the environmental health component of outbreak investigations (often called environmental assessments), to identify outbreak characteristics associated with contributing factor identification. These analyses showed that outbreak contributing factors were more often identified when an outbreak etiologic agent had been identified, when the outbreak establishment prepared all meals on location and served more than 150 meals a day, when investigators contacted the establishment to schedule the environmental assessment within a day of the establishment being linked with an outbreak, and when multiple establishment visits were made to complete the environmental assessment. These findings suggest that contributing factor identification is influenced by multiple outbreak characteristics, and that timely and comprehensive environmental assessments are important to contributing factor identification. They also highlight the need for strong environmental health and food safety programs that have the capacity to complete such environmental assessments during outbreak investigations.

The use of clinical profiles in the investigation of foodborne outbreaks in restaurants: United States, 1982-1997.

Improving the efficiency of outbreak investigation in restaurants is critical to reducing outbreak-associated illness and improving prevention strategies. Because clinical characteristics of outbreaks are usually available before results of laboratory testing, we examined their use for determining contributing factors in outbreaks caused by restaurants. All confirmed foodborne outbreaks reported to the Centers for Disease Control and Prevention (CDC) from 1982 to 1997 were reviewed. Clinical profiles were developed based on outbreak characteristics. We compared the percentage of contributing factors by known agent and clinical profile to their occurrence in outbreaks of unclassified aetiology. In total, 2246 foodborne outbreaks were included: 697 (31%) with known aetiology and 1549 (69%) with aetiology undetermined. Salmonella accounted for 65% of outbreaks with a known aetiology. Norovirus-like clinical profiles were noted in 54% of outbreaks with undetermined aetiology. Improper holding times and temperatures were associated with outbreaks caused by Clostridium perfringens, Bacillus cereus, Staphylococcus aureus, and Salmonella, and also with outbreaks of undetermined aetiology that fitted diarrhoea-toxin and vomiting-toxin clinical profiles. Poor personal hygiene was associated with norovirus, Shigella, and Salmonella, and also with outbreaks that fitted norovirus-like and vomiting-toxin clinical profiles. Contributing factors were similar for outbreaks with known aetiology and for those where aetiology was assigned by corresponding clinical profile. Rapidly categorizing outbreaks by clinical profile, before results of laboratory testing are available, can help identification of factors which contributed to the occurrence of the outbreak and will promote timely and efficient outbreak investigations.