Fundamental Food Microbiology, Third Edition - Fuad Fathir

384 FUNDAMENTAL FOOD MICROBIOLOGY
E. Food Association
Food contaminated with fecal matter of infected people directly (from food handlers)
or indirectly (via sewage and polluted water) is the main source of both hepatitis A
and NLV outbreaks. Infected food handlers, even without symptoms, can contaminate
ready-to-eat food with fecal matter. Vegetables (salads) can be contaminated
with polluted water. Shellfish (oysters, clams, mussels, and cockles) harvested from
water polluted with sewage and eaten raw or improperly heated before eating have
been implicated in many outbreaks of both types of viruses. The virus can survive
in shellfish for a long time. Depuration (in tanks filled with disinfected saline water)
or relaying (kept in unpolluted water in the sea) for self-cleaning of the viruses from
the digestive tracts of the shellfish may not be very effective for hepatitis A and
NLVs. 37–39 In the U.S., the major cause of foodborne viral disease outbreaks is the
contamination of ready-to-eat foods because of poor personal hygiene and contaminated
equipment used with foods served at delicatessens, cafeterias, and restaurants.
1,2
F. Prevention
The two major preventative methods of foodborne virus infections are to kill the
viruses in contaminated foods and adopt good sanitation and personal hygiene habits
to control contamination. Proper heat treatment, such as pasteurization, is enough
to kill the viruses. Steaming lightly to open the shellfish may not be an effective
heat-treatment procedure. Hydrostatic pressure processing, currently being used to
open the shellfish, can also destroy the viruses if the pressure used is above 300
MPa. As indicated before, depuration and relaying may not be effective. Sanitation,
using oxidative agents such as hypochlorite, can kill viruses in contaminated equipment
or in water used in food processing. Good personal hygiene and keeping
suspected individuals away from handling ready-to-eat food will also be important
to control viral foodborne infections. 37 Vaccination against hepatitis A is available
and is used to control the disease.
G. Detection Method
Because enteric viruses do not multiply in food and are usually present in food
in relatively low numbers, their detection from a contaminated food poses difficulties.
Initially, the viruses are concentrated from a suspected food. For identification
of hepatitis A virus, specific cell culture procedures and immunological
methods have been developed. The recently developed reverse transcription-polymerase
chain reaction (RT-PCR) nucleic acid amplification methods are effective
in detecting both hepatitis A and NLVs from shellfish. In one such method, the
viral RNA is amplified with hepatitis A or Norwalk-like viral-specific primers by
RT-PCR, using a viral RNA internal standard control. By this method, a total of
10 2–3 viruses were detected in suspected food samples (e.g., ham, turkey, and roast
beef). 40