Investigation of probable Salmonella outbreak in the National Cancer Institute, Sri Lanka
Authors: Gunasekara Samanmalee P , Mendis Dhanushka , Pathirage Sujatha 
Published: October 2024

Background

An outbreak is the occurrence of case of disease in excess of what would normally be expected in a defined community. Outbreaks in immune compromised population can lead to devastating morbidity and mortality. Infection prevention and control (IPC) team has a pivotal role in both averting and managing outbreaks in health care settings. There were 7 cases of Salmonella spp, isolated from blood and stools since 12th July 2023 up to 11th August. Assuming of a possible outbreak, IPC team decided to investigate in order to find a possible source for the outbreak.

Methods

As soon as the outbreak was confirmed, immediate relevant control measures were taken after studying the available information. Working case definitions was constructed with clinical criteria and laboratory criteria with restrictions by time, place and person. Different categories of case definitions were used as the diagnosis was uncertain, such as “confirmed”, “probable” and “possible”. Active surveillance was conducted to collect information on additional case. Data collection tool was prepared with demographic information, clinical information and risk factor information. Then more cases were detected and line listing was created to organize important information for the investigation. Epidemic curve was drawn to see the pattern of spread and it was an irregularly jagged curve which interprets as intermittent common source epidemic.

Specific control and prevention measures were implemented. Inquiries were made regarding the dietary intake of the patients over the last seven days and it was difficult to find a common source of food item however, all patients have consumed food prepared in the hospital kitchen. Therefore an audit was conducted in the hospital kitchen to identify probable source. Kitchen staff was educated about the food safety measures and personal hygiene. Kitchen staff was screened for Salmonella carrier state in their stool. Quality of the water from the kitchen and wards was checked for fecal contamination. No residual food was available for microbiological testing.

Hypothesis was formulated to gather information after discussion with patients and staff. Findings were communicated to all relevant parties including Director and clinicians in the hospital.

Salmonella isolates were sent to the Enteric Reference Laboratory, Medical Research Institute, Colombo for serotype identification.

Results

It was difficult find a common source. There were some malpractices in the kitchen and those were corrected immediately. Water quality in the hospital was satisfactory. Kitchen staff were not colonized with salmonella. However egg supplier to the kitchen was changed recently and eggs were supplied last minute and the eggs were not washed prior to cooking.

Three isolates sent to the reference laboratory were identified as Salmonella Weltevreden, one as Salmonella Enteritidis, while the remaining three isolates could not be identified to serotype level with the available resources.

Conclusion

The exact contributory factor to the outbreak remained elusive. However, numerous food safety issues which can lead to cross contamination during the preparation of food were identified. Consequently, prompt investigation and control measures are essential to prevent further food borne outbreaks.