How to avoid infections when you have a weak immune system

The most common known cases of moulds in foods causing health problems  are cases of mycotoxin poisoning (aflatoxicosis) caused by eating foods contaminated with fungi such as Aspergillus are well known, and are particularly associated with improperly-stored maize and peanuts in regions where infrastructure is lacking. Outbreaks can kill hundreds of people or animals. However these are not caused by the fungus infecting the patient, but rather by chemical mycotoxins that build up as the fungus grows on the stored grains and nuts.

Far rarer than this are cases of invasive fungal infections in patients who have a much reduced (immunocompromised) ability to fight off infections, including fungal infections caught directly from food and drink. A recent search of the scientific literature (read it here) found 11 examples of invasive fungal infections caught from foods such as Greek yoghurt, home-brewed beer and various dairy products. They found a 5-person outbreak of Rhizopus microsporus in a blood cancer unit in Hong Kong, as well as three cases of pulmonary Aspergillus fumigatus that were suspected as coming from cooked rice in a sterile hospital unit in France. The fact that only 11 examples were found in the whole of the scientific literature shows it is extraordinarily rare, and that even those with very weak immune systems have no cause to worry. 

On the other hand, some doctors recommend following a ‘neutropenic diet’ to minimise the risk of catching bacterial infections from food in patients who are severely immunocompromised (e.g. those having chemotherapy or transplants). Read more at Bloodwise or the British Dietary Association. The neutropenic diet advises patients to avoid higher-risk foods: rare meat, raw sushi, raw egg and dairy, unpasteurised pâté, raw honey, reheated rice, and foods that have been prepared and then left out (e.g. doner kebabs, buffets, salad, deli counter foods). However, scientific evidence to supporting this is generally lacking. One very recent study (read it here) of 150 children having chemotherapy found it was no better than normal food safety guidelines, but was more difficult and expensive to follow.


There are several sensible hygiene measures you can take to avoid bacterial infections while immunosuppressed:

  • Make sure cooked food (especially meat) is piping hot before eating, especially when reheating
  • Clean the inside of your microwave regularly – including the roof
  • Wash the tops of cans before opening them
  • Avoid water fountains and water coolers
  • Consider using individual sachets instead of re-sealing large containers
  • Consider eating at home until you have finished your treatment


Diet is a controversial topic that generates strong feelings in a lot of people, especially among patients with chronic diseases who are (understandably!) desperate for a way to feel better in themselves. Thousands of unscrupulous websites promise incredible effects from cutting out wheat/dairy/yeast, or eating only ‘natural’ foods, or taking unregulated supplements. It’s ok to experiment to find out whether certain foods make you feel better or worse, but it is important to do it safely:

  • Be suspicious of anyone who promises a miracle cure if you buy their book or supplements
  • Discuss any supplements or major changes in diet with your doctor
  • Always keep the original packaging of any supplements in case you have a bad reaction
  • Diets and supplements can also have negative effects (even if they’re marketed as ‘natural’), and they cannot replace the treatments prescribed by your doctor


You can also reduce your risk of infections by getting any vaccinations recommended by your doctor (although live vaccines may need to be given before you start immunosuppressive treatment). The NAC generally recommends aspergillosis patients should be vaccinated against Haemophilus Influenza B and Pneumococcus, and get an annual vaccination against influenza virus (flu).