Typhoid fever spread from asymptomatic restaurant worker in Colorado

On September 11, 2015, a single case of typhoid fever, caused by Salmonella Typhi infection, was reported to the Colorado Department of Public Health and Environment (CDPHE).

symptoms_of_typhoid_feverBecause the patient (patient A) had symptom onset September 2 and had traveled internationally for 4 days 60 days before symptom onset, the case initially was thought to be travel-associated* (1,2).

On October 1, a second case of S. Typhi infection was reported in patient B, with symptom onset September 20. Patient B reported no international travel or contact with ill persons or known carriers. Patients A and B resided approximately 6 miles (10 kilometers) apart and had no discernible epidemiologic connection. Family members of patients A and B tested negative for S. Typhi. CDPHE and the Weld County Department of Public Health and Environment (WCDPHE) investigated to 1) determine whether these cases represented a larger outbreak, 2) identify common exposure sources, and 3) stop transmission. Investigators determined that the typhoid fever in both patients and in a third patient (patient C) was associated with eating in the same restaurant during a 5-day period.

CDPHE defined a case of typhoid fever as clinically compatible illness with isolation of S. Typhi during July 1–October 15 and identification of an isolate with one of two pulsed-field gel electrophoresis (PFGE) outbreak patterns that differed by one band. A carrier was defined as a person who had contact with patients, reported no recent illness, and had S. Typhi with either of the PFGE outbreak patterns in an isolate from a rectal swab or stool specimen. Case finding included searching PulseNet for other isolates that might have been associated with the Colorado cases (3). On October 13, CDPHE issued a health alert notification to clinicians, local public health authorities, and laboratories to be vigilant for additional cases and to encourage reporting. During October 1–9, CDPHE and WCDPHE used the Salmonella National Hypothesis Generating Questionnaire (4), credit card receipts, food recall, shopper card records, and social media to identify potential exposures shared by patients A and B during the 60 days preceding symptom onset. Investigators found that the two patients had fresh produce purchases from the same grocery stores and had six common restaurant exposures.

On October 19, CDPHE was notified of a third Weld Country resident who had tested positive for S. Typhi infection. Patient C had symptom onset September 15 and reported no recent travel or relation to patient A or B. Patient C was interviewed using the Salmonella questionnaire, and credit card receipts were reviewed. Patient C did not shop at the same grocery stores as patients A or B, but all three patients had eaten at restaurant A during August 16–20, 2015. Patients A and C were hospitalized. Isolates from patients B and C had indistinguishable PFGE patterns (pattern 2), and the isolate from patient A had a 1-band difference (pattern 1), which met the PFGE outbreak definition.

s.typhi.symptomsCDPHE hypothesized that a chronic S. Typhi carrier might be working in food service at restaurant A, where food is prepared using fresh ingredients. Possible transmission routes were investigated through environmental assessments and staff interviews; food service staff members were asked to be tested for S. Typhi. Environmental assessments performed on October 27 found no deficiencies in hand hygiene or other food handling issues. Administrators from restaurant A provided a list of all current and former employees who worked in food handling during August 10–August 20, 2015. These more conservative dates were chosen because food might have been served as many as 4 days after preparation, and because of concerns regarding the accuracy of credit card statement dates.

On October 28, current restaurant employees were confidentially interviewed at a local clinic by CDPHE and WCDPHE regarding international travel, symptoms, and work tasks. Because bacterial shedding can be intermittent, employees were requested to collect rectal swab specimens from themselves on October 28 and November 3 for culture and PFGE testing of isolates. All employees were allotted paid time to be interviewed and provide specimens. By October 29, a total of 28 (100%) current employees had responded and provided one or more rectal swab specimens. On October 30, CDPHE was notified by the state health laboratory that S. Typhi had been isolated from one employee. The isolate’s PFGE pattern was indistinguishable from outbreak pattern 1, the pattern of patient A.

Interviews with the infected restaurant worker revealed travel to a country with endemic typhoid fever 15 years earlier, but no recent symptoms, and no contact with any ill persons. The worker was excluded from food service work, treated with azithromycin for 28 days, and monitored with stool testing until three consecutive specimens obtained ≥1 month apart were negative for S. Typhi (2). Restaurant A agreed to keep the worker’s job open and allow him to return to work once he was no longer a carrier.

Typhi infection is a nationally notifiable condition; in Colorado, reporting is required within 24 hours of case detection. Notable clinical symptoms of typhoid fever include insidious onset of fever, and headache, constipation, chills, myalgia, and malaise (1). Unlike other Salmonella species, S. Typhi does not commonly cause diarrhea, and vomiting typically is not severe (1).

Typhi infection is endemic in many low-income countries; an estimated 22 million cases and 200,000 deaths occur each year (2). In the United States, approximately 5,700 cases of typhoid fever are reported annually; the majority occur among travelers (1). In Colorado during 2009–2014, on average, six cases of confirmed typhoid fever were reported annually; all cases were associated with international travel or attributed to a household member or close contact with a carrier. Humans are the only reservoir for S. Typhi; disease is transmitted via the fecal-oral route, typically by contaminated food or water. Chronic carriage occurs in 2%–5% of cases (1,2), and shedding of S. Typhi in chronic carrier stools can be intermittent.

This investigation highlights the potential for chronic S. Typhi carriers to cause illness in other persons, even years after infection. When cases of typhoid fever not associated with travel are detected, rapid and thorough interviewing is essential. Social media posts and credit card receipts to detect common exposures can be useful. The high cooperation rate among workers at the restaurant, which is rare in foodborne outbreak investigations, was attributed to the restaurant’s support and accommodation, demonstrating the importance of collaboration among local public health, state public health, public health laboratories, patients, and industry for successful investigations.

Typhoid fever outbreak associated with an asymptomatic carrier at a restaurant ― Weld County, Colorado, 2015

MMWR Morb Mortal Wkly Rep 2016;65:606–607. June 2016, DOI: http://dx.doi.org/10.15585/mmwr.mm6523a4.

Jessica Hancok-Allen, Alicia B. Cronquist, JoRene Peden, Debra Adamson, Nereida Corral, Kerri Brown


Employees fingered in Norovirus outbreak linked to bread

A massive norovirus outbreak amongst school children in Japan has been, according to health authorities, linked to three factory staff who handled bread as part of their jobs. Japan News reports that norovirus was detected in stool samples of the three staff members – signs of the virus were not founds in an additional 16 food handlers who also submitted samples.hlebozavod-0024

The bakery is suspected to have been the cause of a mass food poisoning that affected many primary schools in the city, according to the Hamamatsu city government.
The city government announced Sunday that workers at Hofuku, a company that produced bread deemed to be the cause of the norovirus outbreak, were found to be infected with the virus.

Yoshinao Terada, chief of the city government’s living and health section, said at a press conference, “It is highly likely that persons with the virus took part in the production process leading to contamination of the bread.”

The company ordered the three workers to stay home from work and specialists began sterilizing the plant. 

Asymptomatic norovirus carriers have been linked to lots of outbreaks in the past.  It’s also possible that the individuals were ill, recovered, and still shedding viruses in their stool. My NoroCORE colleague Robert Atmar and colleagues reported in 2008 that noro could be recovered from folks infected with the virus for up to 56 days (with a median of 28 days) – long after symptoms subsided.

Regardless, there are some hygiene issues going on at Hofuku.

The role of asymptomatic food preparers: 3 norovirus outbreaks in Europe

Norovirus outbreaks are becoming better recognized and are popping up in diverse scenarios.

Today’s issue of Eurosurveillance presents three different norovirus outbreaks, each with its own investigative twists and turns. Excerpts from the three reports are below.

Mayet et al., report that on April 13/11, the medical service of a French military parachuting unit reported an outbreak of acute gastroenteritis involving 147 persons among the military personnel. Meals suspected to have caused the outbreak (pasta and some raw vegetables) were tested for norovirus by PCR. The same norovirus (genogroup I) was found in some of the food items consumed by the cases and in a cook who prepared the meals.

At French military base canteens, meal items are routinely sampled and samples are kept for five days. We tested for norovirus the water of the drinking fountains and the food items served and sampled in the canteen on 11 and 12 April, which were suspected to be associated with the outbreak following the analytical study. The extracted RNA was tested for norovirus by real-time RT-PCR [3]. Pasta was tested by culture for Bacillus cereus which was initially suspected to have caused the outbreak by the physicians who treated the cases. In addition, water from the drinking fountain was tested by culture for coliform germs. For logistical reasons, no samples were requested from the cases, apart from a cook who had prepared the meals and who had fallen ill before the outbreak. The stool sample from the cook was tested for norovirus by PCR as described.

This norovirus-related food-borne disease outbreak involving 147 cases occurred during a parachuting exercise on the night of 12 April and affected significantly the activities of the military unit. It is interesting to note that another outbreak of acute gastroenteritis occurred between 10 and 12 April among residents of a retirement home in the same geographical area, in which the same cook involved in the outbreak in the military unit prepared food on 9 and 10 April. However, the outbreak in the nursing home was only suspected after interrogation of the ill cook; it had not been reported to the health authorities and consequently, it had not been investigated, but it is likely that it was also caused by norovirus considering that around 50% of acute gastroenteritis outbreaks in industrialised countries are related to this agent. Other norovirus outbreaks related to raw vegetables have been described in the past in other military units. The episode described here illustrates once more that food-borne disease outbreaks can easily occur in such settings and stricter hygiene measures may need to be considered.

Guzman-Herrador et al., report that 56 people were affected with gastroenteritis after attending a one-day meeting in a high-quality hotel in the centre of Oslo, Norway, at the end of January 2011. A complete outbreak investigation was carried out. The microbiological investigation confirmed that the outbreak was caused by norovirus. All participants at the meeting were invited by email to complete an online questionnaire asking for information on demographic data, symptoms and food consumption. The results of the epidemiological investigation of the food items served were inconclusive and the source and transmission route of this outbreak remains unclear. However, the environmental investigation highlighted several irregularities in the kitchen that may have enabled the spread of the virus. Specific cleaning procedures and rules were set up for the kitchen staff. As a consequence of this outbreak investigation, the hotel is planning to change its internal routine protocols, for example, samples of food items served at every meal during an event will be stored.

The irregularities that the Food Safety Authority’s inspection found in the kitchen may have enabled the spread of the virus. Handling of ready-to-eat foods by infected food handlers is commonly identified as a contributing factor in outbreaks caused by norovirus. However, the role of kitchen employees or food handlers in the outbreak reported here remains unclear since none of those in the hotel reported any symptoms to the Food Safety Authority and no information was available regarding the health status of the food handlers who produced some of the food items outside the hotel. The importance of identifying asymptomatic food handlers shedding the virus is also well described in the literature: such people can also be a contributing factor in norovirus outbreaks. We do not know if asymptomatic food handlers were involved in the spread of the virus in this outbreak as the employees were not asked to provide stool samples.

Finally, Nicolay et al., report that in March 2009, the Department of Public Health in Dublin, Ireland, was notified of a cluster of four gastroenteritis cases among people who attended a family lunch in a Dublin hotel. A retrospective cohort study was carried out. An outbreak case was defined as an attendee who developed diarrhoea and/or vomiting in the 60 hours following the lunch. Of 57 respondents, 27 met the case definition. Consumption of egg mayonnaise, turkey with stuffing or chicken sandwiches were each associated with increased risk of gastroenteritis. An environmental investigation established that before notification of the cluster, there had been unreported gastroenteritis among staff at the hotel. The earliest symptomatic person identified was a staff member who had vomited in the staff toilets but had not reported it. The sandwiches had most likely been contaminated by three asymptomatic kitchen food handlers who had used the same toilets. Stool samples were submitted by eight cases and 10 staff members. All eight cases and three asymptomatic food handlers on duty at the lunch tested positive for norovirus genogroup II.4 2006. Our analysis suggests that asymptomatic food-handlers can be responsible for norovirus transmission.