National outbreak of Salmonella serotype saintpaul infections: importance of Texas restaurant investigations in implicating jalapeño peppers

Abstract

Background: In May 2008, PulseNet detected a multistate outbreak of Salmonella enterica serotype Saintpaul infections. Initial investigations identified an epidemiologic association between illness and consumption of raw tomatoes, yet cases continued. In mid-June, we investigated two clusters of outbreak strain infections in Texas among patrons of Restaurant A and two establishments of Restaurant Chain B to determine the outbreak's source.

Methodology/principal findings: We conducted independent case-control studies of Restaurant A and B patrons. Patients were matched to well controls by meal date. We conducted restaurant environmental investigations and traced the origin of implicated products. Forty-seven case-patients and 40 controls were enrolled in the Restaurant A study. Thirty case-patients and 31 controls were enrolled in the Restaurant Chain B study. In both studies, illness was independently associated with only one menu item, fresh salsa (Restaurant A: matched odds ratio [mOR], 37; 95% confidence interval [CI], 7.2-386; Restaurant B: mOR, 13; 95% CI 1.3-infinity). The only ingredient in common between the two salsas was raw jalapeño peppers. Cultures of jalapeño peppers collected from an importer that supplied Restaurant Chain B and serrano peppers and irrigation water from a Mexican farm that supplied that importer with jalapeño and serrano peppers grew the outbreak strain.

Conclusions/significance: Jalapeño peppers, contaminated before arrival at the restaurants and served in uncooked fresh salsas, were the source of these infections. Our investigations, critical in understanding the broader multistate outbreak, exemplify an effective approach to investigating large foodborne outbreaks. Additional measures are needed to reduce produce contamination.

Figure 1. Restaurant A-associated cases by date of meal (top) and diarrhea onset (bottom).

Black bars represent 25 confirmed cases. Grey bars represent 22 probable cases. The exact dates of diarrhea onset are not available for 4 probable cases.

Figure 2. Restaurant B-associated cases by date of meal (top) and diarrhea onset (bottom).

Solid black bars represent 16 confirmed cases with meal date-matched controls. Solid grey bars represent 5 probable cases with meal date-matched controls. The dashed black and grey bars represent 5 confirmed and 4 probable cases, respectively, that were not included in the matched analyses because they had no meal date-matched controls.

Figure 3. Cases by date of onset in multistate outbreak and dates of pepper harvest.

The blue bars represent 1500 cases in the multistate outbreak of Salmonella Saintpaul infections reported from 43 states and the District of Columbia, and Canada; these data are modified from reference 6. The orange bar represents the period of serrano pepper harvest (April 18 through May 31) on the farm from which the outbreak strain was isolated. The green bar represents the period of jalapeño pepper harvest (April 14 through June 14) on the same farm. Jalapeño and serrano peppers might begin to wrinkle and lose quality as early as three weeks after harvest (indicated by dashed lines to the right of harvest periods), but refrigeration might extend their shelf life well beyond three weeks (FDA, personal communication).