Food Safety News recently reported on an extensive outbreak of Salmonella Enteritidis (SE) infection among workers consuming egg-fried rice served in a company canteen. The event was documented in a peer-reviewed journal* describing the investigation and laboratory studies. 

During March 2021, 225 out of 334 workers developed fever, diarrhea and abdominal pain after consuming a mid-day meal that included egg-fried rice. Investigation showed that cooking time and temperature for the dish were inadequate and that the product was contaminated with raw egg in non-cleaned mixing bowls.  Laboratory studies including PFGE and WGS confirmed the commonality of the SE isolate from patients and from the menu item as served.  It was significant that all twenty isolates showed extensive resistance to ampicillin, sulfasoxazole, tetracycline and streptomycin.  The isolates were however sensitive to ciprofloxacin, gentamicin and azithromycin.

An interesting observation was that the earliest onset of symptoms following the meal was one hour extending to 38 hours with an average incubation period of 14 hours. The one-hour incubation period is suggestive of some other cause for onset of symptoms or alternatively inaccurate reporting by the patient.  Previously an outbreak of SE occurred on a BA Concorde flight from Heathrow London airport with passengers reporting symptoms shortly before and subsequent to landing on a flight of just over three hours in duration.  The vehicle of infection was identified as hors devours prepared by the airport commissary but also involving 1st Class cabins on other flights of longer duration.

The authors implicated contaminated shells as in introducing SE into the prepared dish.  This observation is in part erroneous given that SE is transmitted principally by the vertical route.  No trace-back was mentioned in the article, so presumably the flock of origin would have persisted as a source of infection.  The specific outbreak was the result of improper handling and incomplete cooking of the egg-fried rice dish incorporating eggs from a presumably SE positive flock.

* Zhang, Y et al. A severe gastroenteritis outbreak of Salmonella enterica, serovar Enteritidis, linked to contaminated egg-fried rice, China 2021. Frontiers in Microbiology.doi.org/10.3389/fmicb.2021.779749 (November 22, 2021)