What is a Nosocomial Infection?

People visit the doctor to get well, right? But many unwittingly go to the doctor's office or hospital to get sick. How's this possible?

Nosocomial infections are infections acquired in a health care environment (also called hospital-acquired or healthcare-associated infections), and both patients and health care workers are at risk. Current estimates by the CDC (Centers for Disease Control) indicate that more than two million people (10% of US patients) fall victim to a nosocomial infection each year, and 90,000 afflicted die.

Transmission of Nosocomial Infections

• In a health care environment, anyone can easily become exposed to pathogens from ill patients. And many of these microbes are especially tough; resistant to antibiotics and other antimicrobial agents frequently used in health care establishments.

• The weakened immune system of patients who are ill is also a factor. In other words, if your immune system is busy fighting off an infection, it has fewer resources available to battle new invaders.

• Transmission of pathogenic (disease causing) microbes can easily occur between sick patients and health care workers moving from room to room, patient to patient.

This may seem like a bizarre concept, after all, people who are sick seek out medical care in order to get better. But think about it. When you enter a health care establishment, be it a doctor's office or hospital, who do you find there? A bunch of sick people. Yet you really need to go to the doctor when you are sick. So how do you protect yourself? It helps to understand the different types, or categories of nosocomial infections.

Exogenous Nosocomial Infections

Exogenous infections are from pathogens acquired in the health care environment, where there is a high concentration of sick people carrying pathogenic microbes, and where health care workers come in contact with multiple patients, potentially spreading those infections.

Endogenous Nosocomial Infections

Endogenous infections are those acquired from normal microbiota (the usually harmless microbes that normally live on our bodies) which have 'gone rogue' in the health care environment, where people often have compromised immune systems and are more vulnerable to opportunistic infections (infections resulting from microbes that are normally harmless, but always ready to take advantage and cause infection if the opportunity presents itself).

Iatrogenic Nosocomial Infections

Iatrogenic literally means 'doctor induced'. These are a type of nosocomial infection that results from modern medicine itself-catheters, surgery and other invasive medical procedures can introduce bacterial into axenic (sterile) areas of the body.

Superinfections

Certain infections can actually result from the use of antibiotics (drugs designed to combat bacterial infections). Since our bodies are covered with normal microbiota (microbes that normally live in and on our bodies without causing us harm). These normal microbiota aren't typically harmful. They even help protect us from infection from other microbes that can cause disease (pathogens). At the very least, normal microbiota take up space and resources on our body, and if 'good-guy' microbes are taking up space, 'bad guy' microbes have a more difficult time establishing themselves and causing infection.

When we take broad spectrum antibiotics, which indiscriminately wipe out good and bad microbes, we inadvertently remove the competition-providing pathogens with a competition-free environment in which to thrive, and selecting for antibiotic resistant bacteria. Clostidium diffucile (C. diff) infections are an excellent example of this is phenomenon. Normal microbiota prevent C. diff from persisting and thriving in the colon. A painful condition called pseudomembranous colitis can result when antibiotic resistant C. diff are allowed to flourish in the aftermath of antibiotic treatment.

Sources

Bauman, R. (2007). Microbiology with Diseases by Taxonomy. Pearson Benjamin Cummings.

Bauman, R. (2004). Microbiology. Pearson Benjamin Cummings.