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Food Focus November 2007

Hepatitis A

Worldwide, hepatitis A infection is very common. In developing countries, high incidence is linked to poor hygiene and sanitation and 90% of children become infected by the age of six without showing symptoms

Hepatitis A is a food- and water-borne virus. Being a notifiable disease, your doctor must report it to the Medical Officer of Health in your local Public Health Unit.

The virus is transferred primarily via the faecal-oral route (people not washing their hands after using the toilet). It will not grow in food or water but is extremely hardy, able to survive on food more easily than on many other products. The disease causes liver damage.

Symptoms and treatment

The virus infects cells of the liver, which are in turn destroyed by the body’s immune response, reducing the liver’s function. The disease takes between two and six weeks to incubate and for symptoms to appear. Initial symptoms are general and include fever, fatigue, headache, nausea and vomiting, followed by jaundice (evident from weeks four to seven after infection). Viral particles are shed from the body in faeces from week three for a further five weeks.

Rest and a low-fat diet is the recommended treatment and you may be out of action for several weeks. Relapses are common, hospitalisation can be as high as 13%, and the disease can be fatal.

Workers and family in close contact with the infected person may be offered an injection of antibodies (gammaglobulin) for temporary protection, and immunisation is recommended for long-term protection and for travellers.

Rate of infection and transmission

There were 122 cases of hepatitis A notified in 2006 representing 2.9 cases per 100,000 people, double the rate from 2005. Almost half had been abroad. The disease affected both men and women equally, with more outbreaks in children. Two outbreaks (many people infected) may have been foodborne.

Any prepared food can be a vehicle for faecal contamination by infected food handlers (who may not show symptoms). Fresh fruit or vegetables washed with water contaminated by sewage, or grown in contaminated soil, can be a significant route of exposure. The risk offered by these pathways is minimised in New Zealand through education and implementation of food safety programmes by growers. Person-to-person exposure is also common, eg, in day-care centres or institutions.

Destroying the virus

The hepatitis A virus is very stable and not destroyed easily by heat or acid conditions but it can be inactivated with a high-pH (basic) solution, eg, pH10 achieved with chlorine, and somewhat reduced with certain types of irradiation. The virus survives in the environment for at least three months and remains viable at cold temperatures and low humidity (eg, in the fridge or freezer) for several years.

Prevention and control

Maintaining scrupulous hygiene is the best way to maintain safe foods and premises because the virus is so hard to destroy and because of the long time gap between infection and the appearance of symptoms.

Risk-reducing activities include:

• effective hand washing

• avoiding direct handling of food by infected food handlers

• thoroughly washing all fruits and vegetables in potable water

• safe harvesting of shellfish from clean waters

• boiling, filtering or chemically treating non-potable water for drinking

• washing any linen used by an infected person in hot water and detergent.

Thorough hand washing (and drying) with soap and water limits the spread from hands on to food or other surfaces.

A critical factor for controlling transmission is to prevent infected people from returning to work too soon following the cessation of symptom – within seven days of onset of jaundice. This is because the virus may still be transferred after symptoms have cleared up.