Regional investigation of a cyclosporiasis outbreak linked to imported romaine lettuce – Nebraska and Iowa, June–August 2013

Abstract

A regional, multistate investigation into a June-August 2013 cyclosporiasis outbreak was conducted in Nebraska, Iowa, and neighbouring states. Cases were confirmed on the basis of laboratory and clinical findings. Of 227 cases in Iowa (n = 140) and Nebraska (n = 87) residents, 162 (71%) reported dining at chain A/B restaurants - 96% reported house salad consumption. A case-control study identified chain A/B house salad as the most likely vehicle. Traceback was conducted to ascertain production lot codes of bagged salad mix (iceberg and romaine lettuce, red cabbage, and carrots) served as house salad in implicated restaurants. A single production lot code of salad mix supplied by both a common producer and distributor was linked to the majority of confirmed cases in persons reporting regional chain A/B exposure. The salad mix linked to illnesses contained imported romaine lettuce from two separate single-grower fields-of-origin and ⩾1 additional field from another grower.

The Hurdle Approach–A Holistic Concept for Controlling Food Safety Risks Associated With Pathogenic Bacterial Contamination of Leafy Green Vegetables. A Review

“…Identification of the offending produce enables subsequent trace-back investigations, which can identify potential suspects responsible for the original contamination further upstream within the value network (Horby et al, 2003; Slayton et al, 2013; Public Health England (PHE), 2015; Buss et al, 2016a,b). However, there have only been two outbreaks for which bacteria matching the outbreak strain have been isolated from environmental samples on, or in close proximity to, suspected farms (CDC, 2006; Grant et al, 2008; Söderström et al, 2008).…”

Cyclospora cayetanensis

“…Additional outbreaks of cyclosporiasis in both countries, and Europe were associated with consumption of basil, lettuce, field greens and snow peas (Herwald et al, 1997;Ho et al, 2002;Doller et al, 2002;Hoang et al, 2005;Insulander et al, 2010;Kozak et al, 2013;Gibbs et al, 2013;Abanyie et al, 2015;CDC, 2014CDC, , 2015Buss et al, 2016) (Table 2). In the US, outbreaks occurred in 25 states in the summer of 2013, with most cases in Texas, Iowa, and Nebraska (Abanyie et al, 2013).…”

Multistate product traceforward investigation to link imported romaine lettuce to a US cyclosporiasis outbreak – Nebraska, Texas, and Florida, June–August 2013

“…Producer A romaine lettuce from two Mexico-origin single-grower ranch lots previously implicated in the Nebraska/Iowa regional investigation [5] was traced forward to define entirety of US distribution for comparison to national distribution of ill persons. All names used herein to list growers, the producer, distributors, and lot codes of various shipments have been anonymized.…”

“…Given known shipping dates and 14-day shelf-life, grower R/ranch R/lot R romaine-containing products were likely not served before 5 June and possibly served up to 17 June [5]. Accordingly, illnesses in other states potentially associated with such common-source romaine would likely have had onset dates in a similar time period as established for associated cases in Iowa and Nebraska, i.e.…”

“…In three Texas and three Florida metropolitan areas, nine and three residents reported illness onsets on or before 8 June, respectively (including Texas city 1, n = 6). In each of these locations, distributors had received producer A shipments on 27-28 May 2013 of romaine lettuce from grower R/ranch R/lot Q, the field-of-origin of romaine lettuce that was linked to two Iowa cases with illness onsets before 9 June [5]. Four additional Nebraska residents (two reporting chain A/B exposure) also reported illness onsets before 8 June and all resided within the service area of the distributor X Nebraska hub which had also received grower R/ranch R/lot Q romaine [5].…”