Volume 45 Number 7
Nosocomial? Waterborne Routes of Hospital-Acquired Infections
Nosocomial? Waterborne Routes of Hospital-Acquired Infections Kelly A. Reynolds, MSPH, Ph.D.
In the United States, microbiological organisms are common to tap water meeting the highest treatment and regulatory standards. While some of these organisms may be harmful to healthy individuals, others are considered acceptable “normal flora” of general water supplies but may cause serious disease in severely immunocompromised persons. Hospitals serve food and water to some of the most susceptible populations to chronic and deadly infections. Conservatively, it’s estimated one in 10 hospitalized patients will contract an infection from the hospital environment itself. These acquired infections are termed “nosocomial” and are a great concern to health care providers.
Microbes of concern
These organisms are typically opportunistic pathogens and may be present in low numbers in drinking water but survive and grow within the distribution system, biofilms and storage tanks. Opportunistic pathogens aren’t considered harmful to most individuals, only causing disease in immunocompromised hosts (i.e., the very young, elderly and those with chronic infections or prior illnesses) and often only in severely ill hosts. Opportunistic pathogens responsible for the majority of nosocomial infections are primarily transmitted via contaminated medical devices, aerosolization or contaminated hands and surfaces. Rarely are these organisms transmitted via the gastrointestinal tract from actually drinking the water.
Who’s at risk?
Assessing individual risk is important in determining the best preventative approach to minimizing waterborne nosocomial disease. Two presenters2 at the NSF International/World Health Organization symposium on HPC Bacteria in Drinking Water in Geneva in April 2002 provided a description of various levels of immunosuppression and respective protection measures related to drinking water quality. A summary of the results of their working group, “Hygienic measures in immunocompro-mised patients,” is listed below:
Protection level I:
Protection level II:
Protection level III:
Protection level IV:
While the preceding descriptions offer a starting point for control of nosocomial disease transmission via a waterborne route, specific categories preclude many susceptible individuals. For example, the general population is relatively resistant to Legionella infection; however, in addition to hospital patients, people with chronic health conditions (i.e., chronic obstructive pulmonary disease, diabetes, heavy smokers and drinkers) may also be affected by exposure to Legionella. Therefore, an individual assessment of risk is critical to determine feasible and necessary protective limits.
Patients may be exposed to harmful waterborne organisms via bathing, showering and drinking water. In addition, hands and medical equipment washed or rinsed in tap water are known to be a source of transmission. For some organisms, i.e., Cryptosporidium, even small concentrations can have a significant impact on the exposed population. Consider that a level of one Cryptosporidium oocyst per 1,000 liters (L) of drinking water is enough to cause 6,000 infections per year in a city the size of New York.1 For most opportunistic pathogens, large numbers of bacteria are required to become problematic.
Most nosocomial waterborne infections are a result of aerosolization or open wound infection of opportunistic pathogens, not the gastrointestinal route. Even in cases of systemic immune deficiency, the protective status of the gastrointestinal tract is often intact.
An ounce of prevention
Although standards and regulations exist for control and prevention of water contamination in community water supplies, no specific regulations exist for protection of special populations from waterborne nosocomial infections. A major concern in the drinking water industry is the ability of opportunistic pathogens to proliferate in the distribution system, biofilms and some point-of-use water treatment devices. A four-step approach to prevention of nosocomial waterborne infections is recommended:1
1. Reduce exposure—Minimize all immunocompromised patient’s exposure to tap water, regardless of documented presence of opportunistic organisms. This simple measure of control has proven effective for reducing the level of legionellosis, cryptosporidiosis and other nosocomial waterborne infections. Drinking water should be purchased sterile or boiled for three minutes. Distillation is also effective. Showers should be replaced with sponge baths.
2. Education of staff and patients—Implementation of existing infection control measures, i.e., hand sterilization, equipment sterilization and aseptic techniques.
3. Targeted surveillance—Monitoring infection rates of nosocomial illnesses and contamination levels of water system supplies.
4. Other measures—Heat treatment of water, i.e., maintain hot water at >60°C (although risk of scalding increases). Establish a maintenance schedule to repair and disinfect contaminated water systems at hospital sites including storage tanks, distribution lines, and filtration systems.
Public health agencies have issued several advisories to immunocompromised populations. For example, following a large outbreak of Cryptosporidium, the U.S. Environmental Protection Agency and the Centers for Disease Control and Prevention (CDC) issued guidelines for prevention of waterborne protozoan infections in the immuno-compromised. The recommendations stated the immunocompromised should only consume water that’s bottled sterile, submicron filtered or boiled.
Furthermore, the CDC recommends hospital water supply systems are routinely maintained and a sterile water source be considered for immunocompromised populations. The CDC also recommends high-risk patients minimize exposure to activities that may aerosolize harmful microorganisms. The CDC targeted stem cell transplant patients, suggesting use of sterile water for drinking, hygiene practices and rinsing medical treatment devices. These patients are encouraged to forego showering and exposure to faucet water.
Municipal tap water supplies, limited by conditions of water stagnation and biofilm build-up in distribution pipelines, fail to meet water quality needs of hospital wards serving severely immunocompromised patients. The best methods of control include the use of sterile water for high-risk populations, treated at the point-of-use. Effective and low-cost water sterilization methods (i.e., boiling for three minutes) are readily available in this country and have proven effective for preventing nosocomial waterborne infections.
2. Glasmacher, A., and S. Engelhart, “Protection of immunocompromised patients from waterborne infections,” Presented at the NSF International/ WHO symposium on HPC Bacteria in Drinking Water, Geneva, Switzerland, April 22-24, 2002.
3. Rusin, P.A., et al., “Risk assessment of opportunistic bacterial pathogens in drinking water,” Reviews in Environmental Contamination Toxicology, 152: 57-83, 1997.
About the author
Table 1: Some common opportunistic pathogens found in drinking water