Risk in Brief


Recently, outbreaks of human swine influenza (influenza A/H1N1) have occurred in Mexico and United States and subsequently the disease has spread to other continents. There are death cases reported in Mexico , United States , and some other countries. The Centres for Disease Control and Prevention (CDC) has determined that the virus is highly contagious and is spreading from human to human. The World Health Organization (WHO) has raised the level of influenza pandemic alert to Phase 5 on 29 April 2009 indicating that a pandemic is imminent. In view of the recent case of human swine influenza in Hong Kong , the emergency response level under the Government's Preparedness Plan for Influenza Pandemic was activated on 1 May 2009 . This brief reviews the current situation regarding the outbreak of human swine influenza as well as advice for the public and trade.

Human Swine Influenza and Swine Influenza

  1. The human cases of human swine influenza are caused by a new influenza A/H1N1 virus not previously detected in swine or humans. The virus contains a mix of swine, human and avian influenza virus genes. Humans infected by the virus will present symptoms similar to those of human flu such as fever, cough, sore throat, body aches, headache, chills and fatigue. Some patients have also reported diarrhoea and vomiting. According to WHO and CDC, human-to-human transmission of the influenza A/H1N1 can occur in the same way as seasonal flu occurs among people, mainly through coughing or sneezing of people infected with the virus. People may also become infected by touching objects soiled with flu viruses and then touching their nose or mouth.

  2. Recently, the Canadian Food Inspection Agency has found the virus in a swine herd in Alberta . The virus may come from a Canadian who had recently returned from Mexico and had been exhibiting flu-like symptoms. International organisations have recommended on step up disease surveillance in pigs and implementation of biosecurity measures.

  3. Swine influenza (distinct from the influenza A/H1N1 in humans) is a respiratory disease of pigs caused by type A influenza virus that regularly causes outbreaks of influenza among pigs. The mortality in pigs tends to be low, while the morbidity is high. There are four main influenza type A virus subtypes that have been isolated in pigs: H1N1, H1N2, H3N1, and H3N2. However, most of the recently isolated influenza viruses from pigs have been H1N1 viruses. Sporadic human infections with swine influenza do occasionally occur. Most commonly, human cases of swine influenza happen in people with direct exposure to or close contact with infected pigs (e.g. workers in the swine industry). The symptoms of swine influenza in humans are usually similar to those of human seasonal influenza, which include fever, fatigue, loss of appetite and coughing. Some people infected with swine flu may also have runny nose, sore throat, nausea, vomiting and diarrhoea.

Safety of Pork and Pork Products

  1. As stated by WHO, influenza viruses are not known to be transmitted through eating processed pork and other products derived from pigs. Heat treatments commonly used in cooking meat (e.g. internal temperature of 70°C) will readily inactivate any viruses potentially present in raw meat products. The pork and pork products handled in accordance with good hygienic practices will not be a source of infection.

  2. In addition, meat from sick pigs or pigs found dead should not be processed or used for human consumption under any circumstances.

Advice to the Public

  1. Maintain good personal hygiene, keep hands clean and wash hands promptly especially after sneezing or coughing. Alcohol-based handrub is also effective when hands are not visibly soiled.
  2. Wear mask when symptoms of respiratory tract infection or fever develop. Refrain from work or school and seek medical advice promptly.
  3. Cook pork thoroughly with internal part reaching at least 75°C before consumption.
  4. Maintain good hygienic practices including washing hands thoroughly before and after handling raw meats.
  5. Step up cleansing and disinfection of residential premises.

Advice to People in Regular Contact with Pigs

  1. Minimise contact with sick pigs and report such animals to relevant animal health authorities.
  2. Sick animals and animals that died from disease should not be slaughtered. Proper hygiene precautions should be taken when handling and disposing of sick or dead pigs.
  3. Maintain good personal hygiene, good hygienic practices during slaughtering and post-slaughtering process to prevent exposure to disease agents. Swine workers should wear protective attire, such as face shield and protective clothing and then disinfect their shoes, clothes and hands after work.
  4. Seek medical attention if any symptoms of influenza-like illness develop and refrain from work.
  5. Step up cleansing and disinfection of workplace.

Advice to Food Trade

  1. Meat from sick pigs or pigs found dead should not be processed or used for human consumption under any circumstances.
  2. Step up cleaning, inspection and maintenance for all ventilating systems in the premises, including air outlets, air filters, fresh air inlets and ventilating ducts.
  3. Step up cleansing and disinfection of the toilets, walls, floors, utensils, tables, chairs and equipment on the premises.
  4. Cleanse and disinfect commonly-used facilities and equipment at least daily by using household bleach (1 part of household bleach in 99 parts of water). Leave for 15 to 30 minutes and then rinse with water. When resources allow, facilities and equipment with high usage rate (such as door knobs, escalator hand rails, lift buttons, etc) should be disinfected at least once every two hours.
  5. If places or facilities are contaminated with respiratory secretion, vomitus or excreta, wipe them away immediately. Then disinfect the surface and neighbouring area by using household bleach (1 part of household bleach in 49 parts of water), leave for 15 to 30 minutes, then rinse with water.
  6. Remind staff developing influenza-like symptoms such as fever, sore throat and cough to cease work immediately and consult a registered medical practitioner.

Risk Assessment Section
Centre for Food Safety
May 2009