AIDS TREATMENT UPDATE, Issue 38, February 1996
Edward King

The guidelines address three ways of preventing infections:

- avoiding initial exposure to the infection - preventing a first episode of disease by primary prophylaxis or vaccination - preventing recurrence of disease by long-term maintenance therapy (secondary prophylaxis)

This article summarises the advice on avoiding initial infection.

PREVENTING EXPOSURE

Most of the diseases that affect people with HIV are caused by either an initial infection with a pathogenic (disease-causing) organism, or by the reactivation of a pre-existing latent infection. There are various steps you can take to try to avoid exposure to the organisms and reduce the risk of becoming infected.

The new guidelines break down exposure risks into five categories:

- sexual exposure - environmental and occupational exposure - pet-related exposure - food and water-related exposure - travel-related exposure

SEXUAL EXPOSURE

Using condoms during sex will help to prevent transmission of a number of viruses, as well as HIV itself. Viral infections that can be transmitted during sex include cytomegalovirus (CMV), which can cause blindness, gut ulcers and other symptoms in people with low CD4 counts; human papillomavirus (HPV), which causes genital warts and is linked to cervical and anal cancer; herpes simplex virus (HSV), which causes lesions in the genital and anal regions; and Epstein-Barr virus (EBV), which is associated with lymphomas in people with HIV.

CMV and EBV are relatively common and easily transmitted viruses, and many people become infected in childhood before they are sexually active. A blood test can tell if you have not yet been exposed. If not, it would be worthwhile taking care not to acquire them.

Sexual practices that may involve exposure to faeces, such as oral-anal sex (rimming), may lead to hard-to-treat gut infections such as Cryptosporidium, Giardia and amoebiasis (amoebas). All of these can cause severe diarrhoea. Other gut infections transmitted through sex include Shigella, Campylobacter and hepatitis A and B.

ENVIRONMENTAL RISKS

Some people may be at increased risk of certain infections because of the places where they live or work.

People who work in health-care institutions, prisons and shelters for the homeless may be at increased risk of tuberculosis. This is less of a worry in the UK than in the USA, where TB is much more common.

People who care for children or whose own children use child-care facilities may be at increased risk of exposure to CMV, Cryptosporidium and other infections such s hepatitis A and Giardia. These risks can be reduced by good hygiene practices such as regular hand-washing, especially after contact with faeces, urine or saliva.

People whose work or hobbies bring them into contact with animals may be vulnerable to a range of infections. However, the only well-established risk is from young farm animals, which can carry Cryptosporidium.

Certain infections are present in soil. Hand-washing after gardening may reduce the risk of Cryptosporidium and toxoplasmosis, which can cause cysts in the brain.

PET-RELATED RISKS

Although domestic pets can harbour a range of infections, people with HIV are not routinely advised to part with pets, not least because of the psychological benefits they may bring. However, it is advisable to avoid cats and dogs that are less than 6 months old and stray animals, as well as pets that have diarrhoea, since these animals are much more likely to have infections such as Cryptosporidium, Salmonella and Campylobacter.

Cat owners should be aware that their pets may harbour Toxoplasma and the bacterial infection Bartonella (also known as cat scratch disease). Try not to let your cat scratch you or lick open cuts, and try to ensure that it doesn't get fleas, as all of these can transmit Bartonella. Cats that roam outdoors or eat raw or undercooked meat are more likely to become infected with Toxoplasma. The cat's litter tray should be emptied every day, ideally by an HIV-negative person, or at least using gloves.

Reptiles such as snakes or lizards are not recommended as pets, as they carry Salmonella. Use gloves when cleaning fish aquariums to avoid bacterial infections. It's sensible to seek specific advice before obtaining an exotic pet such as a monkey.

FOOD AND WATER

Proper hygiene and thorough cooking are the key to avoiding infections from food and water. Fruit and vegetables should be washed before use and put into boiling water, not cold, to cook. Wash kitchen utensils and surfaces promptly after contact with uncooked meat and poultry, and keep these foods away from other foods.

Raw or undercooked meats, poultry and seafood and unpasteurised dairy products can all carry gut infections. Meat and poultry should be cooked until no longer pink in the middle. Eating undercooked beef is the most common way in which previously uninfected people acquire Toxoplasma. Listeria is relatively uncommon, but is a possibility from soft cheeses and 'ready-to-eat' foods such as hot dogs and cold meat from delicatessen counters.

Tap water occasionally becomes contaminated with Cryptosporidium. Although water companies will issue warnings, those warnings may come too late. Bottled water can also be infected with Cryptosporidium. Filtering water using a fine (less than 1 micrometre) filter will eliminate any risk. After filtering, the water should be stored in a fridge to keep it free from infection, and discarded after 24 hours.

There may also be a risk of Cryptosporidium and Giardia from the water in lakes, rivers and swimming pools.

TRAVEL

The risk of exposure to food and water-borne infections is greater during travel in developing countries. Foods that are generally safe include steaming-hot foods, fruits that you peel yourself, bottled drinks (especially fizzy ones), hot coffee and tea, beer, wine and bottled water.

People who travel to developing countries are at risk of developing travellers' diarrhoea, but it is not standard practice to recommend people with HIV to take antibiotics to prevent this, as the drugs can cause side-effects and may lead to the development of drug-resistant organisms. Nevertheless, taking co-trimoxazole (Septrin) or ciprofloxacin can be effective. If you are already taking Septrin as PCP prophylaxis, this may reduce your risk of traveller's diarrhoea.

It is worth taking a supply of antibiotics and anti-diarrhoea pills with you so that you can treat yourself if you do develop diarrhoea. However, it's important to consult a doctor if you develop severe or bloody diarrhoea, dehydration or fever with shaking.

Check which vaccines you should have for the area you're travelling to. In the USA, people with HIV are advised to avoid live vaccines, with the exception of measles. British advice is that some live vaccines such as polio boosters (but not initial polio vaccinations), mumps and rubella are generally safe for HIV-positive people. Yellow fever vaccine is considered safe for asymptomatic people, but inadvisable for people who have developed symptoms. For more information, see the article in AIDS Treatment Update issue 19.

REFERENCE

The guidelines were published as "USPHS/ISDA Guidelines for the Prevention of Opportunistic Infections in Persons Infected with Human Immunodeficiency Virus: A Summary". Morbidity & Mortality Weekly Report Vol. 44 No. RR-8, 14th July 1995.

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