B02014: The survival and decontamination of viruses on fresh produce

Study Duration: February 2000 to April 2002

Contractor: Camden and Chorleywood Food Research Association (CCFRA)

Fresh fruit and vegetable consumption has increased dramatically over recent years and is seen as an essential part of a balanced diet. Increasingly fresh fruit and vegetables are washed and packaged by the food industry and are sold in a 'ready-to-eat' format, so the microbiological safety of such foods is very important.

Studies have indicated that viruses causing gastroenteritis and, more rarely, hepatitis A maybe transmitted through fruit and vegetables. The produce maybe contaminated with viruses at the site where they are grown by coming into contact with sewage contaminated water or may be contaminated if handled by an infected person (during harvesting, preparation or packaging). It is known that gastroenteritis viruses and hepatitis A virus survive well in the environment and, in the absence of cooking, the consumer may on occasions be exposed to infection.

Fresh fruit and vegetables are washed for the 'ready-to-eat' market by commercial processors. Studies with bacteria have suggested that, although washing reduces the number of bacteria to some extent, the process is not nearly so efficient as methods involving heat that are used for some other products. The Agency funded this research to determine how well viruses survive on fresh produce and to investigate the effect of washing on virus removal from a range of fruit and vegetables.

The main approaches will be to:

• To select model viruses to represent the main virus groups that are likely to cause illness from the consumption of fresh fruit and vegetables produce. A vaccine strain of poliovirus to represent the enteroviruses and hepatitis A, the simian rotavirus SA11 to represent human rotaviruses, and a feline calicivirus to represent the Norovirus group. The bacteriophage MS2 was investigated to determine whether it would be a suitable surrogate for the mammalian viruses. Bacteriophages are easier and safer to work with and do not require cell culture facilities for growth.
• To establish methods for the inoculation and recovery of viruses from fresh produce.
• To determine the survival of viruses on various produce types under a range of conditions.
• To investigate the efficacy of washing/sanitisation procedures in removing viruses from produce.

The major findings of this project were:

• The three-mammalian viruses and the bacteriophages all survived for prolonged periods in buffer at refrigeration temperatures (4°C and 8°C). Prolonged survival on fresh fruit and vegetable produce was also observed although to a lesser extent. Reduction by 1-2 log over a two-week period was a typical range but the reduction varied considerably with the type of produce and virus. Virus survival extended beyond the shelf life of the produce.
• Survival at 22°C was poorer both in buffer and produce, although some virus remained viable on produce, even if held at 22°C for a week or more.
• Use of modified atmospheres did not appear to have an effect on bacteriophage survival.
• Removal of viruses was similar to that found with bacteria using conventional chlorine (100ppm) washing, i.e. typically 1-2 log10. Some combinations of virus and produce types gave more than 3 log10 reduction, whilst work involving poliovirus and bacteriophage MS-2 showed removal less than 1 log10 even with chlorinated water. There may be variation between experiments dependent upon factors such as the batch of produce used and the age of the virus stock. This was not fully investigated but was suggested by the bacteriophage work.
• Chlorine washing (100ppm) on almost all occasions resulted in greater removal than washing with unchlorinated water for all viruses.
• Laboratory scale use of alternative washing protocols for bacteriophage MS-2 removal based upon either peracetic acid or chlorine plus surfactant did not appear promising compared with chlorine alone.
• At pilot scale, using bacteriophage MS-2, decontamination could be achieved within excess of 1 log10 removal in the presence of 200ppm and on some occasions, 20ppm chlorine. The efficiency of sanitisation improved with increasing chlorine levels, although the increase from 20 to 200ppm was no more effective than the increase from 5 to 20ppm. Under the conditions provided, agitation may have marginally improved sanitisation, but increasing the wash time above two minutes had little if any additional benefit.
• The results of survival and washing experiments were essentially similar for MS-2 and the mammalian viruses. This suggests that MS-2 could be considered as a potential model for the behaviour of human enteric viruses in testing the efficacy of washing and decontamination procedures for fruits and vegetables.

Viruses can survive on fresh fruit and vegetables for prolonged periods and in many cases for longer than the shelf life of the product. In laboratory experiments, washing produce with potable water and with chlorinated water removed a proportion of virus present. The research suggests that, in relation to virus removal, chlorinated water is better than potable water alone. Washing with chlorinated water, at levels of chlorine commonly used by the food industry, does not remove all the contaminating virus. If contamination levels are high, it is likely that after washing, sufficient virus would remain to cause infection. Experiments with a bacteriophage suggested that it could be a potential model for human enteric viruses that could be used safely and easily by the food industry in the design and testing of washing protocols.

Seymour I.J. and Appleton, H. Foodborne viruses and fresh produce. Journal of Applied Microbiology 2001, 91 759-773

Zenad K., Appleton H, Staffell L., Paish A and Dawson D. Survival and removal of viruses from fresh fruit and vegetables. Poster presentation at 27th Annual PHLS conference 2002.

CCFRA Washing and Decontamination of Fresh Produce Forum. March 30th 2003. "How well does chlorine control viruses?"

Papers in preparation
1. MS-2 as a possible surrogate for noroviruses
2. Survival of viruses on fresh fruit and vegetables
3. Washing of fruit and vegetables to remove viruses

Project completed - Final report is currently being evaluated by the Agency.

Contact: Email: science@foodstandards.gsi.gov.uk