that occurred among 61 residents of Alpine, Wyoming (total population 470), who drank tap water on one particular weekend. Wild animals had probably contaminated the spring that was the source of the town’s tap water.
An often-overlooked aspect of waterborne infectious microorganisms is that contaminated water can also produce a contaminated food product if that water is used to wash the food. In most cases, water used to wash dirt off fruits and vegetables prior to shipping is not tap water quality and is instead what is referred to as “gray water”: water processed to remove the worst contamination but not microbiologically sterile. In some foodborne outbreaks, the contamination may actually have come from water used to wash the food. At first, vegetarians felt safe because foodborne diseases were so often spread by meat. But nowadays most people concerned with ensuring food safety consider any foods that are consumed raw, such as fruits and vegetables, a potentially more serious threat to public health. If meat or other food is properly cooked, the contamination problem is solved, but even careful washing is not always sufficient to render contaminated raw fruits or vegetables safe.
Modern Medicine as a Source of New Diseases
Modern medicine has made impressive breakthroughs in therapies for many human diseases. Surgeons now routinely transplant new organs into patients whose own organs are failing. Cancer chemotherapy is becoming more and more effective. This progress has come at a cost, however. Transplant patients and patients receiving cancer chemotherapy have suppressed immune systems due to the medications they are taking. This immunosuppression is temporary in the case of cancer patients and ends when the chemotherapy is finished, but transplant patients take their immunosuppressive therapy for life. Also, there are a large number of individuals suffering from infectious diseases, such as human immunodeficiency virus (HIV), that are immunosuppressive. Not surprisingly, these immunocompromised patients can become infected with bacteria never before suspected to be able to cause human disease.
Other bacteria cause disease not because the patient is immunocompromised, but because a physical barrier against bacterial invasion is bypassed. For example, accidental perforation of the colon during surgery releases gut bacteria into tissue and blood. Patients with certain types of respiratory infections may have ventilator tubes inserted to keep their airways open, which can allow bacteria to bypass some of the defenses of the respiratory tract to directly enter the lungs. Likewise, catheters enable bacteria to bypass the normal cleansing flow of urine to gain access to the bladder.
Opportunistic pathogens that normally do not cause disease are able to cause disease because some defense of the body that normally keeps them at bay has been breached, giving them the opportunity to cause infection. For an interesting example of an opportunist from an unexpected source, see Box 1-3. The term “opportunist” makes such bacteria seem somehow less dangerous than “real” disease-causing bacteria. Do not be fooled by the seemingly innocuous nature of the opportunists! In most developed countries, a person is far more likely to die from an opportunistic infection than from the epidemic diseases that serve as the public’s mental image of infectious diseases.
Box 1-3.
Enterprising Bacteria Always on the Alert for New Infection Opportunities
An example of how bacteria can rapidly act to take advantage of new opportunities is provided by an outbreak of pneumonia in an intensive care ward. Many of the patients were very ill and were on respirators to support breathing. The type of respirator being used required that a tube be inserted deep into the airway of the lungs, an ideal conduit to carry bacteria deep into the lung, bypassing the normal respiratory defenses. After a number of previous cases of respirator-associated lung infections, hospital personnel have learned to be very careful not to contaminate the respirator itself or to allow bacterial contaminants to enter the air being forced into the lung.
No one, however, thought about mouthwash. Since patients on respirators are often unable to attend to their own dental hygiene, hospital staff workers use mouthwash to clean and freshen the mouth every day. The cause of the lung infections was identified as Burkholderia (formerly Pseudomonas) cepacia. Although this bacterial species is known to cause infections in people with lung diseases, such as cystic fibrosis, it is generally considered to be a relatively innocuous soil bacterium. In fact, B. cepacia is used as a biocontrol agent to degrade herbicides, such as 2,4,5-trichlorophenoxyacetic acid (2,4,5-T, a toxic defoliant also known as Agent Orange). The bacterium is ubiquitous in soil and water, but in this case apparently managed to contaminate many lots of the mouthwash, which did not contain alcohol to discourage bacterial growth. In effect, the hospital workers taking care of the patients on respirators were inoculating the patients’ teeth and gums daily with a contaminated mouthwash solution, which placed the bacteria in an ideal location to gain access to the lungs.
Source:
Centers for Disease Control and Prevention (CDC). 1998. Nosocomial Burkholderia cepacia infection and colonization associated with intrinsically contaminated mouthwash—Arizona, 1998. MMWR Morb Mortal Wkly Rep 47:926–928.[PubMed]
Another way in which modern medicine has affected the infectious disease picture is by increasing the human life span. The increasing number of elderly people, whose immune defenses are beginning to decline and who are more likely to be receiving therapies that undermine the defenses of their bodies, provides an expanding population of individuals highly susceptible to diseases. Put these elderly people in crowded conditions, such as those experienced in nursing homes, and an even greater opportunity is created for infectious diseases to spread.
Postsurgical and Other Wound Infections
Most recent studies of wound infections have focused on the infections that can be a serious complication of surgery (postsurgical infections). In the preantibiotic era, infections were a major complication of surgery. Regardless of how skillful the surgeon, an infection could kill the recipient of the most successful surgery. This may have been the origin of the grim old joke that the surgery was a success, but the patient died. Antibiotics changed all this and made routine surgery possible because antibiotics eliminated any bacteria that might have managed to penetrate the barrier of the surgical scrub and other hygienic procedures.
The first shadow in this rosy picture appeared when surgeons and other health care workers began taking patient survival for granted and became more lax in their time-consuming hygienic practices. Hospitals trying to save money began cutting budgets for nurses and janitors, individuals responsible for the cleanliness characteristic of hospitals in developed countries. To make matters worse, the bacteria often causing postsurgical problems tend to be resistant to antibiotics. These postsurgical infections have consequences for both patients and hospitals. Patients risk damage to major organs or even death, while hospitals and insurance companies bear significantly higher financial costs to care for these patients.
Not long ago, the state of Pennsylvania made history by publishing postsurgical infection data from its hospitals. Until this unprecedented move to transparency, infection rates in hospitals were secrets guarded almost as fiercely as classified CIA files. The reason is easy to understand. No hospital wants potential users of its facilities, especially people getting elective surgery, to identify the hospital as a place where people go in healthy and come out sick or even dead. The Pennsylvania figures confirmed what everyone in the infectious disease community already knew: patients who contract a postsurgical infection, especially one caused by antibiotic-resistant bacteria, cost over four times more to treat than people who do not contract an infection. Unfortunately, this type of statistic has attracted a lot more attention than the suffering of the patients involved. The good news is that this increased transparency has led to improved antibiotic stewardship and hygiene practices, which in the long run will help individuals who go into hospitals.
Recently, however,
