Preventing diseases from food and water
Preventing Diseases from Food
When travelling or working abroad, transient, minor upset-stomachs are very common. With the best of intentions we can all get caught out: hotel food turns out to be infected, street food safe – whereas usually the opposite is true. Below are some general recommendations that should be considered whilst abroad. Of course if going to an area during an active epidemic such as cholera, bird flu or Ebola, these recommendations become much more important, and potentially lifesaving.
Have food that you can recognise, is well cooked, and eat in a reliable, clean environment.
These things are somewhat self-evident but can be difficult when in an unknown country. ‘Bush meat’ is available in many countries and you may find yourself eating anything from bats or monkeys, to forest animals. Whilst potentially appealing to the adventurous, several fatal illnesses are spread via this route, including Ebola and MERS. This should be especially avoided if entering areas of epidemics.
Clearly well-cooked food presents a much lower risk of disease than rare meat, as the cooking heat destroys the bacterial cell wall, killing the organism. There are a few bacteria, belonging to the specific groups of bacillus and clostridium, which are able to produce heat-resistant spores. Prolonged exposure to temperatures greater than 100 degrees centigrade are often required to kill such organisms.
Avoid street food. Eating in a reputable hotel, or preparing the food yourself, is advised in most circumstances.
Peel and wash fruit and vegetables, boil eggs thoroughly and avoid salads
Fruit and vegetables should be treated with care since many of them are consumed without being cooked. In market situations, where close contact can occur between animals and vegetables, it is especially important to wash them in purified water if infections such as MERS (which is spread by camels) are to be avoided.
As is well known, the organisms Salmonella and Campylobacter are frequently found in raw eggs. Cooking them well, so that there is no ‘runny’ element, ensures that the bacteria are killed.
As salads, prepared by others, are often washed in the local water supply, they can be infected by a host of water-borne diseases. Best avoided.
Drink pasteurised milk and factory produced beverages. Avoid flavoured ice.
Although practised with wine from the 12th century in China, pasteurisation became widespread much later in the 19th Century, with the treatment of milk. Louis Pasteur’s process reduced the bacterial content of milk but didn’t affect the quality of the product unduly. Fresh, unpasteurised milk and cheese are available in many countries and should be avoided – especially by the immunocompromised or pregnant.
It is best to beware of both flavoured ice pops and ice cubes in drinks – as both can be made with local water. Beverages, from beer to orange juice, should be contained in factory-made bottles which have no evidence of tampering.
Preventing Diseases from Drinking Water
Whether travelling or working abroad, diarrhoeas caused by drinking contaminated water are a common occurrence. Although more often inconvenient than medically serious, some water-borne infections can result in significant symptoms such as bloody diarrhoea as seen with shigella, or rarely, a profound dehydration leading to multi-organ failure, as may result from cholera.
Examples of other water-borne infections include typhoid, hepatitis A, cryptosporidium, giardia, campylobacter, salmonella, shigella and E.coli, as well as many viruses.
Bottled or Boiled are Best
Purified water, in factory produced containers, presents a low risk of infection but check that it has not been opened and that if cooled in a bucket of iced water, you are not drinking some drops of bucket water remaining on the container. In fact all ice should be avoided. Even in hotels, care should be taken, as tap-water can often be of uncertain quality, making it wise to even consider brushing teeth in bottled water.
Water boiled vigorously for 1 minute is sufficient to kill bacteria, viruses and organisms which can be difficult to destroy, such as cryptosporidium. Altitude affects the boiling temperature: as altitude increases, atmospheric pressure decreases and water boils at lower temperatures – to be on the safe side, boil water for 3 minutes above 3000m.
Purification Tablets and Filtering Systems
Purification tablets containing chlorine and iodine have been used for many years to make drinkable water, but the difficulties with eliminating organisms such as the long-lived cryptosporidium, has led to the widespread adoption of chlorine dioxide as the agent of choice. Such tablets must dissolve fully in the water and are therefore subject to temperature, requiring several minutes before safe consumption can occur. Always read the instructions.
When larger volumes of water are required, filtering systems, whether portable or permanent, are worth considering. Although less practical for the businessman or traveller, they are often utilised in disaster situations where many workers need protecting from diseases such as cholera, which is a common threat. Such systems often work by sieving the water of particles larger than 1 micron and by binding organisms on to the filter substance – known as adsorption. Such processes are not only dependant on temperature but also the flow-rate of the water being driven through the filter, the latter requiring frequent cleaning or changing to remain effective.
As organisms such as protozoa can be resistant to purification tablets, and small organisms such as viruses, evade filtering systems, both approaches are often utilised sequentially, whereby tablet-purified water is then later filtered for added benefit.
Washing Hands
Many water-borne infections are spread by inadequate hygiene following visits to the toilet. In fact with illnesses such as cholera, in which most infected individuals are well and just ‘carry’ the disease, it is possible to transmit the organism without the presence of diarrhoea. Hand-washing, with an alcohol based solution if available, is essential.