Eurosurveillance

ECDC

Outbreak of Salmonella enteritidis Infections Linked to a District Hospital in Kaunas Region, Lithuania, 2006

 Rediger
  Published: 15.10.07 Updated: 15.10.2007 14:21:44

O. Ivanauskiene, B. Kamorunaite. Kaunas Public Health Centre, Lithuania

Introduction

A hospital outbreak of gastroenteritis due to S. enteritidis occurred from the 25th through the 29th of June 2006 in one district of the Kaunas region. Cases were identified in two hospitals. Food for these two hospitals was prepared by the same food handling unit of one of the two hospitals. Initially, 19 patients were reported with gastrointestinal disease acquired in the hospitals. Of these patients, 16 had a laboratory confirmed diagnosis of S. enteritidis. The Kedainiu branch of the Kaunas Public Health Centre conducted an epidemiological investigation that began on the morning of June 28th, three days after the first cases appeared. It was decided that a full investigation should be conducted to determine the extent of the outbreak and to use a cohort study to identify the cause of the outbreak.

Methods

A retrospective cohort study that included patients and staff at the two hospitals was conducted. Patients admitted to one of the two hospitals in question on June 25th or later who had eaten dishes served in the hospitals and had not shown any symptoms of diarrhoea prior to admission were eligible for inclusion in the study. Staff who had eaten food from the hospital kitchen during the same period were also included..
An exposure was defined as consumption of a food item prepared and served by the food handling workers of hospital A. This kitchen prepared all the food for breakfast, lunch and dinner for the two hospitals.
Patients seeking medical attention for diarrhoea (with or without vomiting) and/or abdominal pain during the three days prior to June 28th were considered to have been suffering from acute gastroenteritis. We defined a probable case as a person who was admitted to the hospital June 25th or later and staff that had eaten dishes served at the two hospitals, and then became ill with symptoms of diarrhoea. A confirmed case was a person as described above with a microbiologically confirmed S. enteritidis infection.
A questionnaire was developed at the Kaunas Public Health Centre using EpiInfo 2000. Interviews were conducted face to face. The questionnaires included inquiries addressing basic demographic data, symptoms, date of clinical onset, duration of illness, seeking additional medical care at the two hospitals and food history using the list of food items available at the hospitals.

Results

The study included 152 indviduals (108 from hospital A and 44 from hospital B), and the questionnaires were completed for all participants in the cohort. A total of 137 were in-patients who had been admitted to the hospitals with other disorders and 15 were hospital workers; all had eaten food from the hospital kichen. In total, 45 people (35 patients and 10 workers) had clinical symptoms of diarrhoea and this fulfilled the criteria of a probable outbreak case (attack rate = 30%). The 35 patients were from different departments at the two hospitals. Stool specimens from 57 people (40 patients and 17 workers, including three asymptomatic kitchen workers from the food handling unit) were microbiologically tested for Salmonella enterica. A total of 41 persons were found to be positive for S. enteritidis (34 patients and 7 workers) and thus fulfilled the definition criteria of a confirmed outbreak case.
Figure 1 shows the epidemic curve. The outbreak lasted from June 25th to 29th, 2006, and peaked on June 26th. The shape of the curve indicates a common point source outbreak.
In addition to diarrhoea, 35 patients (77%) reported nausea, 16 patients (35%) reported vomiting and 34 patients (75%) reported abdominal pains. The mean duration of illness was 5 days. Two patients with severe symptoms of salmonellosis were relocated to the Kaunas 2nd Clinical Hospital where the departments of infectious diseases are located. The other cases were all treated at the two hospitals that experienced the outbreak. All 48 cases recovered following treatment.

Figure 1. Cases of S. enteritidis infection by date of clinical onset, linked to a district hospital in the Kaunas region of Lithuania between June 25th and 29th, 2006 (n=45).

 

 

 

 

 

 

 

We compared the food-specific attack rates (AR) for each food item on the list among the exposed and the non-exposed cohort members usins univariate analysis. There were no specfic food exposures that were significantly associated with an increased risk of illness using a p-value of 0.05. However, consumption of butter and boiled eggs tended to be associated with illness.

Table 1. Food-specific attack rates (AR)

Risk factors / Факторы риска 

Exposure: Yes / Воздействие: Да

Exposure: No / Воздействие: Нет

 

No.

ill / Число заболев-ших

Total  Всего  

AR% КП %

No.ill / Число заболев-ших

Total Всего

AR%  КП %

RR ОР

95% CI / 95% доверит. интервал

p-value / p-значение

Butter / Масло

25

73

34.2

20

79

25.3

1,24

0.89 – 1.73

0.229

Boiled eggs /  Вареные яйца

20

55

36.4

23

95

24.2

1,42

0.93 – 2.16

0.113

Porridge with butter / Каша с маслом

16

108

14.8

10

44

22.7

0,84

0.61 – 1.16

0.241

Milk soup with butter / Молочный суп с маслом

14

105

13.3

10

47

21.3

0,82

0.57 -1.17

0.216

Cutlet (with fresh eggs) / Котлеты (со свежими яйцами)

9

68

13.2

18

84

21.4

0,71

0.40 – 1.24

0.190

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Environmental investigation

 A number of factors were identified during the inspection of the kitchen that may have contributed to the outbreak. Risky food preparation, incorrect storage of food items, expired shelf life and other violations of hygiene requirements for food preparation at the food handling unit were observed.
The kitchen prepared a number of standard food items each day including sandwiches, boiled eggs, different porridges, soups and special meat dishes with fresh eggs. If butter was served with these dishes, it was put direcly on the plates in a way that may have cross-contaminated the dishes. Meals were prepared throughout the working day and some of the refrigeration equipment was out of order. Although local control procedures were in place, the procedures were not being followed and the temperatures of the refridgerators were not logged. Various main courses were kept at warm temperatures creating favourable conditions for growth of microorganisms. There were no means of hand desinfection and drying in the lavatory fasilities used by the food handling personnel. The outbreak occurred during the summer holiday period and thus some of the workers were new, less experienced and lacked hygiene skills.
Samples of water and food, and swabs from surrounding objects were taken for microbiological investigation. The causal agent of the enteric infection  S. enteritidis was detected in a refrigerator where milk products including butter were stored.

Measures taken

The local and regional Governmental Veterinary and Food Safety Services were regularly updated about the situation so that control measures at the food handling unit of the two implicated hospitals could be performed. A number of measures were taken to stop the outbreak:

  1. The food handling unit was closed for cleaning and desinfection from July 5th to 19th, 2006;
  2. Specialists from the Kaunas Public Health Centre organised the final desinfection at the food handling unit, the quality being tested by microbiological and chemical investigation;
  3. The chief of production and the assistant headmaster responsible for providing meals to the patients were fined;
  4. The kitchen workers were enrolled and completed hygiene courses;
  5. It was recommended that the head of the food handling unit should reduce the assortment of dishes;
  6. The Salmonella outbreak and the preventive measures were discussed at a faculty meeting at the hospitals A and B;
  7. The Kedainiu Municipality doctor, television and other media were informed.

Conclusions

The investigation of this outbreak indicated that S. enteritidis had spread due to lack of proper hygiene and improper food preparation by the workers of food handling unit of hospital A that resulted in the cross-contamination of different dishes. Although the consumption of butter was not statistically significantly associated with an increased risk of illness, contaminated butter could be one of the plausible vehicles because it was stored in the contaminated refrigerator.
No subtyping of the outbreak strain was performed. Therefore, it is not possible to know if the strain found in the kitchen was the same as the outbreak strain. This is one limitation of the present study.
S. enteritidis is prevalent in layer flocks, and eggs are a commonly consumed food item that may occasionally be contaminated with S. enteritidis at different rates according to their place of origin. Since raw eggs were stored and used in the kitchen, it is possible that the source of infection was introduced through contaminated table eggs. These problems were then aggravated by cross-contamination of food and improper hygiene while preparing food at the food handling unit.
Consumers need to be aware of the continuing hazard, adopt appropriate control measures and follow advice provided by the Governmental Veterinary and Food Safety Services in order to reduce the risk of outbreaks of S. enteritidis infection associated with raw shell eggs that continue to be a common cause of food-borne illness.

References

  1. Heymann D., Ed. Control of Communicable Diseases Manual. 18th edition; 2004.
  2. Laiškonis A. Infekcinės ligos šeimos gydytojo praktikoje. Kaunas 2002.
  3. Laiškonis A., Bareišienė M., Budnikas V., Vėlyvytė D. Infekcinių ligų žinynas. Kaunas 2004.
  4. Berghold C., Kornschober C., Weber S. A regional outbreak of S. Enteritidis phage type 5, traced back to the flocks of an egg producer, Austria. Eurosurveill. 2003;8(10):195-198.
  5. http://www.wrongdiagnosis.com/medical/s_enteritidis.htm
  6. www.who.dk

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