Typhoid Fever and Paratyphoid Fever

Causative agents

Typhoid and paratyphoid fevers are caused by the bacteria Salmonella Typhi and Salmonella Paratyphi respectively.

Clinical features

Typhoid fever is a systemic infection that can affect many organs. Common symptoms of typhoid fever include prolonged fever, headache, malaise, nausea, abdominal pain, loss of appetite and constipation or diarrhoea (in adults, constipation occurs more often than diarrhoea). In some cases, rose-coloured spots appear on the trunk and enlarged spleen and liver can be detected. In severe cases, there may be life-threatening intestinal bleeding and perforation. Apart from symptomatic patients, some asymptomatic infected individuals are able to shed bacteria in their faeces or urine. In addition, a small number of people, called carriers, continue to shed the bacteria in their faeces after recovery from the disease. Paratyphoid fever presents a similar clinical picture but the illness tends to be milder.

Mode of transmission

Typhoid and paratyphoid fevers are mainly transmitted via the faecal-oral route. The causative bacteria are passed in the faeces and urine of infected people, which may contaminate food, water or beverages and cause infection in those who have consumed the contaminated items. Types of food which are susceptible to contamination include shellfish (particularly oysters), raw fruits and vegetables and unpasteurised milk and dairy products. Transmission through sexual contact, especially among men who have sex with men, has rarely been documented.

Incubation period

For typhoid fever, the incubation period ranges from 3 to 60 days and is usually 7 to 14 days. The incubation period for paratyphoid fever is usually 1 to 10 days.

Management

Infected individuals should seek medical advice for management. The infection can be effectively treated by antibiotics. Symptomatic treatment such as fluid replacement and adequate rest is also important. Strict personal hygiene should be observed in order to prevent transmission of the bacteria to others. The majority of patients can fully recover after treatment. However, about 2 to 5% of patients will become carriers of the bacteria and they may require long-term follow-up.

Prevention

1. Maintain good personal hygiene
   
   • Perform hand hygiene frequently, especially before handling food or eating, and after using the toilet or handling faecal matter
   • Wash hands with liquid soap and water, and rub for at least 20 seconds. Then rinse with water and dry with a disposable paper towel or hand dryer. If hand washing facilities are not available, or when hands are not visibly soiled, hand hygiene with 70 to 80% alcohol-based handrub is an effective alternative
   • Wear gloves and a surgical mask while disposing of or handling vomitus and faeces, and wash hands thoroughly afterwards
   • Exclude infected persons and asymptomatic carriers from handling food and from providing care to children, elderly and immunocompromised people
   • Refrain from work or attending class at school, and seek medical advice if suffering from vomiting or diarrhoea

2. Maintain good food hygiene
   
   Adopt the 5 Keys to Food Safety in handling food, i.e. Choose (Choose safe raw materials); Clean (Keep hands and utensils clean); Separate (Separate raw and cooked food); Cook (Cook thoroughly); and Safe Temperature (Keep food at safe temperature) to prevent foodborne diseases.
   
   Careful procedures of cooking and preparing food
   • Drink only boiled water from the mains or bottled drinks from reliable sources
   • Wash fruits and vegetables thoroughly under clean running water and avoid those with damaged skin
   • Scrub and rinse shellfish in clean water. Remove the viscera before cooking, if applicable.  Heating to an internal temperature of 90°C for 90 seconds is required for cooking of molluscan shellfish. If possible, remove the shells before cooking as they impede heat penetration. Otherwise, boil at 100°C until their shells open; boil for additional three to five minutes afterwards. Discard any shellfish that do not open during cooking
   • Cook food thoroughly
   • Keep the kitchen, cooking and eating utensils clean
   • Use separate utensils (e.g. knife and chopping board) to handle raw food and cooked food or ready-to-eat food

   Hygienic food storage environment

   • Take food promptly after cooking. Perishable foods that has been kept at room temperature for more than 4 hours should be discarded
   • Choose ready-to-eat, cooked or perishable foods that are stored correctly, e.g. hot food at above 60°C, cold food at or below 4°C, frozen food at or below -18°C
   • If perishable food is not consumed immediately, keep it at 4°C or below. Keep it well covered
   • Handle and store raw and cooked food separately. Store raw meat, poultry, and seafood below ready-to-eat food or cooked food in the fridge to prevent juices from dripping onto ready-to-eat food or cooked food 
   • Clean refrigerator regularly. Check the temperature of the refrigerator with a thermometer and ensure the fridge is kept at or below 4°C and freezer at or below -18°C
   • If necessary, refrigerate cooked leftovers and consume as soon as possible. Reheat thoroughly before consumption. Discard any spoilt food items

   * Please visit the website of Centre for Food Safety for more information on food safety.

3. Others
   
   • Immunisation for typhoid fever is not routinely recommended. Even vaccinated individuals should take care to avoid consumption of potentially contaminated food and water as the vaccine does not provide full protection from infection
   • Travellers who visit endemic areas of typhoid fever are advised to consider vaccination. For more information, please visit Travel Health Service website at https://www.travelhealth.gov.hk/