Maine Becomes the Third Outbreak of Salmonella Enteritidis Phage Type 913
Outbreak of Salmonella Enteritidis Phage Type 913 Maine – January, 2002
The EpiGram March 2002,
Maine Bureau of Health’s Division of Disease Control
The Maine Bureau of Health is investigating an outbreak of Salmonella enteritidis (SE) among Maine residents who became ill between 13 January and 26 January 2002. The outbreak was first detected in late January when an unexpectedly large number of Salmonella isolates were reported by clinical laboratorians and were sent to the Maine Health and Environmental Testing Laboratory (HETL) for serotyping.
During 2001, 8 cases of Salmonella were reported between January 1 and February 15, 2001, one of which was S. enteritidis. During the same period in 2002, a total of 22 cases were reported, 16 of which were S. enteritidis. Subsequent molecular testing at the Maine HETL determined that 15 of 16 isolates shared a single Pulsed Field Gel Electrophoresis (PFGE) pattern on one enzyme testing, and that 4 of 5 tested isolates also had a common pattern on testing with a second enzyme. Testing at the Centers for Disease Control’s Foodborne and Diarrheal Diseases Laboratory identified 13 of 15 isolates as sharing the same uncommon phage type (Type 913). These similarities strongly suggest a common source for the illness.
Individual telephone interviews were conducted with all 16 SE cases or with the appropriate parent or guardian, and studies were performed on all SE isolates. One case, in a hospitalized child, was excluded from cluster analysis after interviews revealed that the bulk of his incubation period occurred during overseas travel and that the PFGE pattern did not match the 15 others. The remaining 15 cases were included in the outbreak investigation. Eleven cases reside in southern Maine (York and Cumberland counties) and 4 in the mid coast region (Waldo, Sagadahoc, and Lincoln counties) . Case age range is 5-88 years with a mean of 31 and a median of 25 years. Seventy three percent of cases are female. Dates of illness onset range from January 13-January 26, with 11 cases clustered during the week of January 20-26.
During the investigation, a history of mung bean sprout ingestion emerged in many of the cases.
Nine (60%) specifically recalled a history of eating mung bean sprouts, and one had possible, but uncertain bean sprout consumption history. Five cases did not recall any history of eating bean sprouts on specific questioning. No other food, restaurant or other exposure commonalities were identified.
For the nine cases who consumed bean sprouts, meal-to-illness intervals ranged from 12-103 hours with a mean of 47 and a median of 48 hours. Of these individuals, eight (89%) had eaten bean sprout-containing items in one of 4 Asian restaurants in southern and midcoastal Maine (Pad Thai or raw salad with bean sprouts). The ninth individual ate a chicken wrap sandwich that contained bean sprouts at a non-Asian restaurant. In all, five Maine restaurants were implicated as the source for bean sprout consumption.
Once mung bean sprouts were identified as the probable source of illness for the nine cases, Sanitarians from the Maine Department of Human Services and the City of Portland were dispatched to all implicated restaurants to determine bean sprout providers. Three of the restaurants were noted to have utilized a single bean sprout grower in Maine, designated as Grower A (note: two of the three reported more than one supplier). When a list of customers of Grower A was obtained, it was determined that he had also supplied sprouts to a fourth implicated restaurant, and also to a distributor who supplied these sprouts to the fifth implicated restaurant. Officials from the U.S. Food and Drug Administration (FDA) and the Maine Department of Agriculture were notified, and joined the investigation.Once investigators identified the likely source of seeds used to grow implicated sprouts, the grower voluntarily ceased use of sprout seeds from this stock and recalled previously distributed sprouts grown from implicated seed stock.
Epidemiologists at state health departments in Massachusetts and New Hampshire were contacted and they reported that no concomitant increases in SE incidence in their respective states.
A telephone case-control study was conducted by the Maine Department of Human Services’ Bureau of Health and CDC. Preliminary results further implicate mung bean sprout consumption as the source for Salmonella infection in the 9 cases.
This investigation is continuing with the collaboration of the US Food and Drug Administration and with assistance from the Maine Department of Agriculture. Epidemiological and laboratory assistance has been supplied by the CDC Foodborne and Diarrheal Diseases Branch.
Of note, during February and March 2001, Edmonton, Canada experienced an outbreak of Salmonella enteritidis phage type 913 (SE PT 913), the same unique phage type as this Maine outbreak. Eighty-four cases were reported. Sixty-two percent of cases in Edmonton recalled eating at Vietnamese, Chinese or Japanese style restaurants in the Edmonton area. Of those cases, 84% recalled consuming a meal with bean sprouts. Further investigation revealed that all implicated restaurants shared the same bean sprout supplier during February 2001.
The following was excerpted from CDC MMWR Outbreak of Salmonella serotype Kottbus Infections Associated with Eating Alfalfa Sprouts — Arizona, California, Colorado, and New Mexico, February–April 2001 51(01):7-9- January 11, 2002
Since 1995, 15 outbreaks of Salmonella spp. and two outbreaks of Escherichia coli O157:H7 infections associated with sprouts have been reported to the Centers for Disease Control (CDC). Despite public health advisories about the risks for eating raw sprouts, persons at high risk for systemic infection continue to eat sprouts.
Sprouts may be contaminated during seed production, germination, sprout processing, or consumer handling and preparation. On the farm, sprouts seeds may become contaminated through the use of untreated agricultural water, improperly composted manure as fertilizer, excretion from domestic or wild animals, runoff from domesticated animal production facilities, or improperly cleaned harvesting or processing machines. The association of specific seed lots with illness suggests that seeds are the most likely source for other sprout-related outbreaks. Conditions suitable for seed sprouting also are ideal for increasing pathogenic bacterial counts by several logs.
Public education efforts about the risks for eating uncooked sprouts need to be continued, particularly among vulnerable populations (i.e., the elderly, young children, and immunocompromised persons). CDC and the Food and Drug Administration (FDA) recommend that persons at high risk for systemic infections not eat raw sprouts. For persons who continue to eat sprouts, FDA recommends cooking before eating to reduce the risk for illness.
The Maine outbreak was identified and investigated in a timely manner due to the rapid notification of the cluster of cases by Nordx Labs to the Division of Disease Control. The sooner an investigation can begin, the more likely we are to identify the source and prevent further spread of infection
Other articles about Salmonella PT913 and possibly related to bean sprouts:
“Outbreak of Salmonella Enteritidis Phage Type 913 Gastroenteritis Associated with Mung Bean Sprouts – Edmonton, 2001”, Canada Communicable Disease Report, Volume 27-18, 15 September 2001.
“A Multi-County and Multi-State Outbreak of Salmonella Enteriditis (group D) Among Oriental Restaurant and Market Patrons” Bill L. Toth, MPH, Donna Walsh, RN, BSN, Zuber Mulla, PhD, MSPH, Dean Bodager, RS, MPA, Roberta Hammond, PhD.
“Trace Back, Maine 2002 Salmonella Enteritidis PT913 Bean Sprout Outbreak” Personal Communication, Anthony Yartel, MPH Infectious Disease Epidemiologist, Division of Disease Control, Maine Bureau of Health.