Subsequent to the report on deadly rare fungal infection caused by Rhizopus species in blood cancer patients in a local hospital, there are concerns over food safety in connection with people with lower immunity.

Rhizopus species

Rhizopus species are fungi that are ubiquitous in nature. They can be recovered in profusion from decaying vegetables, fruits and their seeds, grains, compost piles, soil, animal excreta, and moulding bread. Many of these fungi can proliferate in moist environments and are common environmental contaminants. They are occasional causes of fatal infections in patients with weakened immunity.

People with Lower Immunity

  1. Patients with weakened immunity, elderly, pregnant women, young children and infants are susceptible populations in comparison to healthy adults. These people, if infected by common foodborne pathogens, may develop more severe symptoms than just mild ones such as diarrhoea and vomiting.
  2. The weakening of immune system can be due to immunological disorders, such as human immunodeficiency virus (HIV) infection and some chronic diseases (e.g. cancer). Another factor contributing to the weakened immunity is immunosuppressive therapy they received that would decrease the body's immune responses, such as drugs given to prevent transplant rejection or to treat solid tumour.
  3. The natural defense against or ability to withstand an infection, including foodborne infection, declines gradually as people age. In addition, some elderly may further be weakened if they suffer from certain chronic diseases, such as diabetes, as a result of the disease or its therapy.
  4. Hormonal and immunological changes during pregnancy may result in weakening of mother's immune system and hence become more prone to foodborne disease. On the other hand, the developing foetus is susceptible to foodborne pathogens that may not cause symptoms in the mother. Foodborne listeriosis is well-known for causing severe illness to pregnant women, affecting their foetuses.
  5. The natural defenses of infants and young children against foodborne pathogens are weaker. Moreover, the stomach of newborns, especially of premature babies, is less acidic than that of adults. Bacteria and other pathogens survive relatively easier in newborns. In addition, infants and young children consume more food in proportion to their weights than adults. Hence, they can proportionately consume more toxins or contaminants if present in food. Foodborne infections by Escherichia coli O157:H7 in some, especially the very young, may cause acute kidney failure.

Regulatory Control

  1. Some countries have set standards for yeasts and moulds in food, but usually for the purpose of overall hygiene monitoring. None of these standards concerned with specific fungus.
  2. In Hong Kong, there is no legal limit for fungus in food. Since the presence of these microorganisms in food under normal circumstances poses no significant additional risk to normal immunocompetent individuals, the food may not be regarded as unfit for human consumption. Some fungi can form mycotoxins, such as aflatoxin which is governed by the Harmful Substances in Food Regulations (Cap. 132AF). If the maximum concentration of certain substances present in specified foods exceeds that permitted in the Regulations, offenders, upon conviction, shall be liable to a fine of $50,000 and imprisonment for six months.
  3. For food complaint about visible fungal growth in food, the respective samples/ remnants will be tested to ascertain the presence of ‘yeast and mould'. Offenders may be guilty of an offence for sale of food not of the substance as demanded by the purchaser. Upon conviction, the offenders shall be liable to a fine of $10,000 and imprisonment for 3 months.

Advice to People with Lower Immunity

  1. To observe strictly food safety and hygiene, ensure safe food handling, food preparation and food storage.
  2. People with lower immunity (and their caregivers) should follow specific food safety advice given by doctor or dietitian in relation to their health status.
  3. For patients receiving active immunosuppressive therapies or following transplant, a low microbial diet (primarily a cooked-food diet) may be required. Under those circumstances, the advice of attending doctor should be sought.

Advice to Trade

In Hong Kong , all food available for sale in the market must be fit for human consumption and complied with legal standards. The trade should also ensure that food sold or imported are of the nature, substance, and quality of the food demanded by the purchaser.

Risk Assessment Section
Centre for Food Safety
April 2009