Research Report

Emerging Pathogens

Researchers, medical professionals and water utilities remain on the alert for emerging pathogens that imperil public health. In recent years, two such pathogens -- broadly characterized as mycobacteria and microsporidia -- have been recognized as the causes of opportunistic pulmonary (lung) and gastroenteric infections in AIDS and other patients with compromised immune systems. Since water is a common source for both pathogens, there is concern about a more widespread impact on the general population that has been evidenced by some documented cases. The possibility of waterborne or foodborne transmission underscores the importance of water disinfection and good sanitation practices.

Mycobacteria

There are 60 species of mycobacteria, two of which cause tuberculosis and leposy. Several other species, including Mycobacterium avian complex (MAC) and non-tuberculous mycobacteria (NTM), have been associated with respiratory and pulmonary diseases that primarily affect people with AIDS or pre-existing lung conditions. Both organisms result in persistent infections that are difficult to identify and treat, with symptoms sometimes lasting two years or longer. Those infected are advised to boil drinking water, avoid raw foods, and rinse and peel fruits and vegetables.

MAC initially involves the intestinal tract. Symptoms include high fever, persistent diarrhea, weight loss, stomach ulcers, abdominal pain and fatigue. Other parts of the body also may be affected: joints, brain, skin, blood, liver and lungs. As the most debilitating opportunistic infection of HIV/AIDS patients, MAC is a leading cause of death among this group. While MAC and NTM are commonly found in soil and water, they are usually harmless to healthy individuals and are not contagious between people. However, unusual sources have been identified. In one instance, MAC was traced to a hot tub. A young woman, who was otherwise healthy, contracted a pulmonary disease from inhaling MAC-infected aerosols in the mist created by air jets in a hot tub used on a regular basis. MAC also has been traced to hot water in hospitals. It was assumed that patients were exposed by inhalation or ingestion from showers, water used in endoscopies and possibly drinking water. However, finding mycobacteria in a hot tub means that many more individuals could be at risk of contracting an infection.

The lesson of these exposures is the absolute necessity of thoroughly disinfecting or sanitizing hot tubs and hospital surfaces and equipment. Chlorine-based sanitizers are the most efficient and effective weapons against bacteria in these settings, as well as in swimming pools and homes. Further, public water supplies must be adequately disinfected to inactivate these organisms and must include a chlorine residual in the distribution system to prevent recontamination.

Microsporidia

Microsporidia, like Cryptosporidia and Cyclospora, are protozoal pathogens that form spores or oocysts. Their effect on human health has been recognized only in recent years, since the identification of two enterocytozoon (intestinal) species, E. bieneusi and E. intestinalis. These species, plus three rare, nonintestinal forms, are referred to as "human microsporidia." Again, the intestinal organisms primarily affect AIDS patients, but, although difficult to diagnose, they do appear in otherwise healthy people. Epidemiological knowledge of transmission is limited, but it is thought to follow the fecal-oral route from person to person and through food and water contaminated by humans.

Enterocytozoa are more common in developing countries, since they are directly related to sanitation. However, travel and immigration can spread infections anywhere. Some people infected with human microsporidia may suffer from a mild case of diarrhea, but most experience no symptoms at all. Occurrence of chronic diarrhea is most pronounced in AIDS patients and others with weakened immune systems. In those cases, human microsporidia also can spread to the eyes, liver, respiratory tract and kidneys.

In terms of prevention and reducing exposure, only Cryptosporidium is being monitored and reported at present. No guidelines exist for the other intestinal spore-forming protozoa such as those described above, since public health officials and clinicians are just beginning to see evidence of diseases caused by these other organisms.

Research continues in an effort to determine the best water treatment methods to eliminate or inactivate protozoan cysts and oocysts. At present, filtration is considered the most effective removal strategy.