Nosocomial (Healthcare-Associated) Infections
Nosocomial (Healthcare-Associated) Infections
Nosocomial infections—also called healthcare-associated infections—are infections contracted in health-care settings, usually hospitals. Such infections have occurred for as long as doctors have handled patients, but their source only began to be widely understood in the mid-to late nineteenth century. Nosocomial infections occur primarily at sites where objects such as catheters, scalpels, needles, breathing tubes, and similar devices are introduced into the body, providing a place for bacteria to grow. Infections caused in this way are an increasing problem, partly due to the ongoing evolution of resistance to many antibiotics by bacteria. Approximately 1.4 million people worldwide acquire healthcare-associated infections at any given time. These infections claim many tens of thousands of lives every year and occur in both developed and developing nations. Countermeasures include handwashing, glove-wearing, increasing blood-supply safety, improvement of injection practices, immunization of health-care workers and others, and improvement of water supply quality and waste management.
The word “nosocomial” comes from the Greek word nosokomos, meaning “person who tends the sick.” The idea that physicians might themselves be a major cause of disease did not occur until the 1790s, when a few doctors began to notice that puerperal fever, a disease caused by the group-A streptococcus bacterium Streptococcus pyogenes, was afflicting women after childbirth and seemed to be transmitted to patients by doctors. These observations received little attention from the medical world as a whole, however, until the mid-nineteenth century. At that time, puerperal fever was common in hospitals, where S. pyogenes was transmitted by physicians’ unwashed hands as they went from patient to patient. During childbirth, women were often infected with the S. pyogenes that contaminated their doctors’ hands as they moved between patients, or from the autopsyroom directly to the delivery room. This commonly resulted in death rates in maternity wards of 10–25%, with occasional epidemics wiping out entire wards.
In 1843, writer and physician Oliver Wendell Holmes (1809–1904) published a seminal essay titled “The Contagiousness of Puerperal Fever.” In it, he argued forcefully against the widespread medical opinion that puerperal fever was not a contagious disease. “The disease known as Puerperal Fever,” he wrote, “is so far contagious as to be frequently carried from patient to patient by physicians and nurses.” He noted that in case after case, a string of maternal deaths could be traced to a series of visits by a single doctor or midwife. In one instance, he documented a string of deaths 40 cases long—all caused by a single doctor.
WORDS TO KNOW
PUERPERAL FEVER: Puerperal fever is a bacterial infection present in the blood (septicemia) that follows childbirth. The Latin word puer, meaning boy or child, is the root of this term. Puerperal fever was much more common before the advent of modern aseptic practices, but infections still occur. Louis Pasteur showed that puerperal fever is most often caused by Streptococcus bacteria, which is now treated with antibiotics.
RESISTANT ORGANISM: An organism that has developed the ability to counter something trying to harm it. Within infectious diseases, the organism, such as a bacterium, has developed a resistance to drugs, such as antibiotics.
STANDARD PRECAUTIONS: Standard precautions are the safety measures taken to prevent the transmission of disease-causing bacteria. These include proper hand washing, wearing gloves, goggles, and other protective clothing, proper handling of needles, and sterilization of equipment.
Also in the 1840s, Hungarian-German physician Ignaz Semmelweis (1818–1865) documented similar facts in the Vienna General Hospital. The death rate in the section of the hospital in which women in childbirth were attended by doctors was three times higher than that in which they were attended by midwives. Semmelweis concluded that doctors were infecting patients by visiting them with unwashed hands after performing autopsies (dissecting corpses). He managed to institute a program of handwashing using a chlorine solution, greatly reducing the death rate. In the 1860s and 1870s, French scientist Louis Pasteur (1822–1895) established that infectious disease was caused by germs, that is, living organisms too small to be seen by the naked eye. With this discovery, Pasteur finally explained the mechanism by which unwashed hands can transmit disease. By the end of the century, medical opinion had shifted towards a nosocomial origin for puerperal fever. However, there were still many doctors who washed their hands after delivering babies, but not before.
In the twentieth century, nosocomial puerperal fever rapidly became a thing of the past, at least in industrialized countries. However, other forms of nosocomial infection eventually became more common for two reasons. The first is the proliferation of various devices—hypodermic needles, catheters, intravenous lines, breathing tubes, and the like—for delivering air or fluid to or from the body. The second is the rise, especially in health-care settings, of antibiotic-resistant bacteria. Intrusive medical devices and antibacterial drugs have saved many lives that would otherwise been lost, but not as many as they could have saved without the nosocomial infections that accompanied their use.
Nosocomial infections of the respiratory tract, associated with breathing tubes, are the most common; in particular, ventilator-assisted pneumonia is common in intensive-care units. The next most common sources of nosocomial infection, in order of decreasing frequency, are central lines (also called central venous catheters, tubes inserted into large veins and left in place for days or weeks), urinary drainage catheters, and surgical wounds. Two factors combine to cause a typical nosocomial infection. The first is decreased immune-system function in a patient who is already ill, and the second is the introduction of bacteria into the patient, usually by some type of invasive device. The National Nosocomial Infection Surveillance system of the United States Centers for Disease Control and Prevention has found that about 83% of nosocomial pneumonia cases are associated with breathing machines (ventilators), 97% of urinarytract infections are associated with catheters, and 87% of cases of bacteremia (infection of the bloodstream) are associated with central lines.
The most common cause of nosocomial infection is the Staphylococcus aureus bacterium. Some strains of this bacterium have evolved resistance to all penicillin-type antibiotics and others. For example, the USA300 strain of S. aureus, first identified in 2000, has evolved resistance to cefalexin, erythromycin, doxycycline, beta lactams, dindamycin, tetracycline, ciprofloxacin, and mupirocin. When a patient is infected with the bacteria, physicians may need to search by trial-and-error for an antibiotic that will work. During this time, an infection may progress and even kill a patient.
Nosocomial bacterial infections are treated with antibiotics, although antibiotic-resistant strains of bacteria are making this increasingly difficult. Prevention is accomplished through infection control and standard precautions by health-care workers, including handwashing, flushing of catheters and intravenous lines using saline (salt water) solution or other chemicals, wearing disposable gloves, using disposable needles, and properly sterilizing surgical instruments. In 2005, the World Health Organization announced an initiative called the Global Patient Safety Challenge 2005–2006, with the motto “Clean Care is Safer Care.” This was an effort to reduce nosocomial infection risks throughout the world by improving practices related to the purity of blood products, injection practices, water and sanitation, emergency care, and hand hygiene.
Of all patients admitted to hospitals in the industrialized world, between 5% and 10% acquire a nosocomial infection—sometimes more than one. For patients admitted to intensive care (also called critical care, often requiring the use of breathing machines and other high-tech support devices), the rate is between 15% and 40% because these patients are subject to more invasive devices. In poor countries, the nosocomial infection rate for hospital patients is 2–20 times higher (i.e., can approach 100% in some locations). More than half the babies in neonatal care units in developing countries acquire a nosocomial infection, with death rates ranging from 5% to 56%.
Health-care workers may not only transmit nosocomial infections but acquire them. During the SARS (severe acute respiratory syndrome) epidemic of 2002– 2003, health-care workers accounted for 20–60% of cases around with the world, depending on location.
In the United States, as of 2005, 1 out of 136 patients admitted to a hospital became seriously ill from a nosocomial infection. This entailed a caseload of 2 million nosocomially infected patients yearly with an annual monetary cost probably over $5 billion and some 80,000 deaths per year. For comparison, a little over 40,000 people die each year in the U.S. from car accidents. In Mexico, the per capita nosocomial infection rate is somewhat higher: Mexico sees about half the number of deaths from this cause in a population about a third the size of the U.S. population.
According to the medical journal The Lancet, “perhaps the most important topic in infection control is handwashing; yet health-care workers are notoriously bad at washing their hands each time that they should.” Thus, ironically, the same behavioral problem that caused thousands of women's deaths from puerperal fever in the nineteenth century—dirty hands—remains a problem in twenty-first century medicine.
Nosocomial infection is a growing problem worldwide, partly because more patients are suffering serious underlying illnesses, such as AIDS (acquired immunodeficiency syndrome). In many health-care settings in industrialized countries, rushed health care workers often comply poorly with rules for hand-cleansing. In poorer countries, dirty instruments, crowding, lack of safe water sources, and dirty overall conditions also help spread nosocomial infections.
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Diep, Binh An, et al. “Complete Genome Sequence of USA300, An Epidemic Clone of Community-Acquired Meticillin-Resistant Staphylococcus aureus.” The Lancet 367 (March 4, 2006): 731–740.
Pittet, Didier, et al. “Effectiveness of a Hospital-Wide Programme to Improve Compliance with Hand Hygiene.” The Lancet 356 (October 14, 2000): 1307–1312.
Vincent, Jean-Louis. “Nosocomial Infections in Adult Intensive-care Units.” The Lancet 361 (June 14, 2003): 2068–2077.
World Health Organization. “Global Patient Safety Challenge 2005–2006: Clean Care is Safer Care.” 2005. <http://www.who.int/entity/patientsafety/events/05/GPSC_Launch_ENGLISH_FINAL.pdf> (accessed February 20, 2007).