A nosocomial infection is an infection you pick up while receiving care in a healthcare facility, not one you had when you arrived. These are also called healthcare-associated infections (HAIs), and they are surprisingly common: on any given day, about 1 in 31 hospital patients in the United States has at least one. In 2015, an estimated 687,000 HAIs occurred in U.S. acute care hospitals, and roughly 72,000 patients with these infections died during their hospitalizations.
How Nosocomial Infections Differ From Other Infections
The defining feature of a nosocomial infection is timing. The infection was not present or incubating when the patient was admitted. It develops as a direct result of being in a healthcare environment, whether that’s a hospital, surgical center, long-term care facility, or even an outpatient clinic. Hospitals concentrate vulnerable people, invasive procedures, and antibiotic-resistant organisms in one place, creating conditions where infections spread more easily than they would in everyday life.
The Four Most Common Types
The CDC tracks four major categories of nosocomial infections, each tied to a specific medical device or procedure:
- Catheter-associated urinary tract infections (CAUTI) develop when bacteria enter the urinary tract through a catheter, a thin tube inserted into the bladder to drain urine. The longer the catheter stays in, the higher the risk.
- Central line-associated bloodstream infections (CLABSI) occur when germs enter the bloodstream through a central line, a catheter placed in a large vein to deliver medications or fluids. These are among the most dangerous HAIs, with an average additional hospital cost of about $48,000 per case.
- Surgical site infections (SSI) develop in or near the incision after surgery. They can range from a superficial skin infection to a deep infection involving organs or implanted materials.
- Ventilator-associated pneumonia (VAP) occurs in patients on mechanical ventilators, machines that help with breathing through a tube in the airway. The tube can allow bacteria to reach the lungs.
Common Germs Behind These Infections
Several types of pathogens cause nosocomial infections, and many of them are difficult to treat because they’ve developed resistance to standard antibiotics.
MRSA (methicillin-resistant Staphylococcus aureus) is one of the most well-known. It’s a staph bacterium that no longer responds to common antibiotics like penicillin or amoxicillin, which means it requires stronger, more targeted treatment. C. diff (Clostridioides difficile) is another major culprit, causing nearly half a million infections in the U.S. each year. It triggers severe colon inflammation and highly contagious diarrhea, often after a patient has taken antibiotics that wiped out the protective bacteria in their gut. Various gram-negative bacteria round out the list, responsible for bloodstream infections, pneumonia, and meningitis in hospitalized patients.
Who Is Most at Risk
Not every hospital patient faces the same level of risk. Several factors make certain people more susceptible. Older adults and newborns have weaker or less developed immune defenses. Patients with chronic conditions like diabetes, cancer, or organ failure are already in a compromised state. Those receiving treatments that suppress the immune system, such as chemotherapy or drugs given after organ transplants, are especially vulnerable.
Length of stay matters too. The longer you’re in the hospital, the more opportunities there are for exposure. Patients in intensive care units face the highest risk because they tend to have the most invasive devices (ventilators, central lines, urinary catheters) and the longest stays. Any break in the skin, whether from surgery, a catheter, or even a bedsore, creates a direct entry point for bacteria.
The Financial and Human Cost
Beyond the health consequences, nosocomial infections add significant cost to a hospital stay. According to the Agency for Healthcare Research and Quality, the average additional cost per infectious HAI case is approximately $31,000. The range varies widely by type: a catheter-associated urinary tract infection adds roughly $13,800, while a central line bloodstream infection or ventilator-associated pneumonia can each add close to $48,000. These costs reflect longer hospital stays, additional treatments, and the resources needed to manage complications.
For patients, this translates to more time in the hospital, additional procedures, and a slower, more difficult recovery. In some cases, especially with drug-resistant organisms, the infection can become life-threatening even when the original reason for hospitalization was routine.
How Hospitals Work to Prevent Them
Prevention relies on a combination of strict protocols and daily vigilance. Hand hygiene is the single most important measure. Every interaction between a healthcare worker and a patient is a potential transmission point, so consistent handwashing before and after contact is the foundation of infection control.
For procedures involving catheters and central lines, hospitals use what are called “care bundles,” checklists of steps that must all be followed together. For a central line insertion, this includes full sterile barriers (mask, cap, gown, sterile gloves, and a full-body drape), cleaning the insertion site with an antiseptic solution, choosing the insertion site that minimizes infection risk, and placing a sterile dressing over the site afterward. Once the line is in, staff scrub the access port before each use and perform daily checks to determine whether the line is still needed. Removing unnecessary devices as soon as possible is one of the simplest and most effective ways to reduce HAIs.
For surgical patients, prevention includes proper skin preparation before incisions, maintaining sterile conditions in the operating room, and careful wound care afterward. ICU patients may be bathed daily with antiseptic solutions to reduce the bacteria on their skin.
What Patients and Families Can Do
You’re not powerless in this process. If you or a family member is hospitalized, ask healthcare workers whether they’ve washed their hands before touching the patient. This is a reasonable, recommended question that most providers welcome. If you have a catheter or central line, ask each day whether it’s still necessary. Keep the area around any surgical wound clean and watch for signs of infection: increasing redness, warmth, swelling, drainage, or fever. Reporting these symptoms early gives the care team the best chance of catching an infection before it becomes serious.