Pathogenic Bacterial Contaminations in Hospital Cafeteria Foods

MATERIALS AND METHODS

Study area: The study was undertaken using cafeteria located in Mahasarakham hospital between April and September of 2008. Mahasarakham hospital is a major public hospital located in the centre of Mahasarakham province, Thailand. From statistic data in 2008, Mahasarakham hospital has 1,157 admissions/day, 472 beds, 62 doctors, 390 nurses and 1,094 general staff members.

Aerobic plate count: Forty different types of foods (33 ready-to-eat foods and 7 freshly-made foods) were purchased from hospital cafeteria and immediately examined for bacterial contaminations. The foods were processed according to the guideline of Bacteriological Analytical Manual (BAM) of US Food and Drug Administration (FDA). Fifty grams of each food were mixed with 450 mL of nutrient broth (resulting in a dilution of 10^-1) and blended until it became homogenate. The original homogenate was further diluted to be 10^-3, 10^-4, 10^-5 and 10^-6 using nutrient broth and 0.1 mL of diluted homogenate was spread on nutrient agar. The plates were incubated at 35° for 24-48 h. The total aerobic colonies were counted and calculated as colony forming units per gram of food (cfu g^-1). Each food sample was tested in triplicate.

Bacterial identification: Four selective media were used for presumptive identification of pathogenic bacteria: Bismuth Sulfite Agar for Salmonella typhimurium, MacConkey Agar with Sorbital for Escherichia coli, Mannitol Salt Agar for Staphylococcus aureus and Bile Esculin Azide Agar for Streptococcus faecalis (all media were purchased from Criterion, Hardy diagnostics, CA, USA). The cafeteria foods were processed as for aerobic plate count and each diluted food homogenate (0.1 mL) was spread on the four different selective media agar plates. The positive colonies grown on selective media agar were subcultured on nutrient agar and used for further identification by gram staining and appropriate biochemical tests according to the guideline of BAM (FDA). Each food sample was tested in triplicate. The commercial ATCC strains of bacteria (Salmonella typhimurium ATCC^® 14028, Escherichia coli ATCC^® 25922, Staphylococcus aureus ATCC^® 25923, Streptococcus faecalis ATCC^® 29212) were used as positive controls throughout the experiment.

RESULTS

The data from total aerobic plate count (Table 1) showed that, of 33 different ready-to-eat foods, the majority (54.54%) were found to be contaminated with bacteria >10⁷ cfu g^-1, whereas 36.36% of them had bacteria around 10⁶-10⁷ cfu g^-1. Only 9.10% of ready-to-eat foods were contaminated with bacteria <10⁶ cfu g^-1. In contrast, of 7 different freshly-made foods, the majority (71.42%) were found to have bacteria <10⁶ cfu g^-1 (Table 1).

Table 1:	Percentages of foods with different levels of aerobic bacterial plate count (cfu g-1)
Ready-to-eat foods are referred to the foods that have been cooked in advance and can be eaten when purchased; Freshly made foods are referred to the foods that have been cooked only when ordered

Table 2:	Percentages of foods contaminated with identified strains of bacteria
Ready-to-eat foods are referred to the foods that have been cooked in advance and can be eaten when purchased; Freshly made foods are referred to the foods that have been cooked only when ordered

In addition, most of ready-to-eat foods (57.57%) were found to be contaminated with Escherichia coli, followed by Streptococcus faecalis (51.51%), Staphylococcus aureus (48.48%) and Salmonella typhimurium (27.27%), respectively (Table 2). Up to 42.85% of freshly-made foods were found to be contaminated with Staphylococcus aureus, followed by Escherichia coli and Streptococcus faecalis at equal percentage (14.28%) (Table 2). None of freshly-made foods were found to be contaminated with Salmonella typhimurium.

DISCUSSION

There are several investigations for food- borne nosocomial outbreaks that only focused on foods served in hospitals (Dhiraputra et al., 2005; Graham et al., 2002; Lund and O'Brien, 2009; O'Brien et al., 2001; Shetty et al., 2009; Winter et al., 2009) but the foods brought from outside hospitals have not been widely regarded as a cause of food- borne nosocomial infections. However, the foods from outside hospitals that usually remain unchecked by healthcare workers have often been served to vulnerable patients. Therefore, they are likely to be a link to food-borne nosocomial infections as well. The results from examination of foods sold in Mahasarakham hospital cafeteria, Thailand, showed that pathogenic bacterial contaminations were much higher in the ready-to-eat foods than in those that were freshly-made (Table 1). The ready-to-eat cafeteria foods were also found to be contaminated with Escherichia coli, Staphylococcus aureus and Streptococcus faecalis at similar rates (Table 2). Up to half of the ready-to-eat foods were contaminated with two or more strains of these pathogenic bacteria (data not shown). The pathogenic bacteria contaminated in hospital cafeteria foods could be transmitted to patients via several routes. Firstly, the visitors who may bring contaminated food from the hospital cafeteria to the patients for consuming. It is a general custom in Thailand that the visitors often bring food as a gift for better wellbeing or as a patient’s request and bringing foodstuffs from outside hospitals to patients is generally not forbidden. Also, Thai healthcare workers, especially nurses in public hospitals, are often required to overwork due to shortages of staff and they do not generally have time to examine the foodstuffs the visitors bring to patients. If such food is heavily contaminated with bacteria, the patient who consumes it or is in contact with it could possibly be infected and perhaps cause nosocomial infection outbreak. Although, there was no record in Thailand regarding the prevalence of nosocomial outbreak because of the food brought from outside hospital and such prevalence can be difficult to determine due to the lack of effective surveillance system, the data elsewhere have shown that there are several outbreaks within hospitals due to the foods brought from outside hospitals, for example, the home-prepared Chinese meal that caused outbreaks of Salmonella enteritidis gastrointestinal infections among medical staff (Metz et al., 2001) the ready-to-eat sandwiches and scalded sausages that caused Listeria monocytogenes infections among patients (Graham et al., 2002; Shetty et al., 2009; Winter et al., 2009) and the home-baked cream-filled cakes that caused Escherichia coli O157 outbreak among both medical staff and patients (O'Brien et al., 2001). The outbreak of Salmonella sp. that directly associated with hospital cafeteria has also been reported (Johnson et al., 2001). Secondly, since, poor hand-hygiene compliance have been observed among Thai healthcare workers and visitors (Patarakul et al., 2005) if the visitors or healthcare workers consumed contaminated food at the hospital cafeteria, their hands, clothes, or other items may be contaminated with pathogenic bacteria and they could transmit these bacteria to patients, perhaps resulting in nosocomial infections. There were several reports showing that the contaminated items might transmit the pathogenic strains of nosocomial bacteria, for instance, coins (Tolba et al., 2007) clothes, wristwatches, wedding rings, neck ties (Dancer, 2010) and mobile communication devices (Brady et al., 2009). These contaminated items might serve as vehicle for pathogenic bacteria and thus lead to staff-to-patient or patient-to-patient transmission. Nonetheless, there is still no conclusive evidence to suggest the relationship between the contaminated items and the spread of pathogens in hospital environment. Lastly, if the visitors and healthcare workers are infected due to contaminated cafeteria food, they may unintentionally be carriers or reservoirs of pathogens. The asymptomatic healthcare workers have been reported to be responsible for prolonged outbreaks of nosocomial infections (Ben-David et al., 2008; De Vries et al., 2006; Occelli et al., 2007). As this study suggested that as much as 43% of freshly-made cafeteria foods were free of Escherichia coli, Staphylococcus aureus, Streptococcus faecalis and Salmonella typhimurium contaminations (data not shown), health authority should thus educate and encourage hospital cafeteria staff to provide more choices of freshly-made foods and to reduce cooking ready-to-eat foods. This may help reducing the risk of nosocomial infection outbreaks.

CONCLUSION

This study showed the high levels of pathogenic bacterial contaminations in foods available in Mahasarakham hospital cafeteria. The routine check of sanitary of foods sold in hospital cafeteria could help to reduce the possibility of patients being exposed to pathogenic bacteria and therefore the incidence of nosocomial infections.

ACKNOWLEDGMENT

We thank to Mahasarakham University Research Unit for funding this research (grant No. 5201029).