Nosocomial Infections


Infections acquired during a hospital stay are called nosocomial infections. Formally, they are are defined as infections arising after 48 hours of hospital admission. For earlier periods it is presumably assumed that the infection arose prior to admission, though this is not always going to be true. Patients with only a brief hospital stay may find they have a nosocomial infection after leaving hospital.

Nosocomial infections are common with estimates at about 10% of American hospital patients, or more than 2 million cases annually in the USA. Death rates may be 20,000 annually in the USA although some estimates are as high as 88,000 deaths. Cost estimates are as much as $4.5 billion in 1995.

Hospitals generally have a high rate of nosocomial infections and the reasons are rather obvious. There are a lot of sick people around, many with depressed immune systems, and a lot of staff that deal with them every day. Nosocomial infections may arise from inhalation of droplets in the air or spread by direct hand contact from hospital staff or visitors. Most nosocomial infections afflict patients with reduced immune response either due to age, serious disease, certain medications, or recent surgery.

Types of nosocomial infections: There are various types of nosocomial infections affecting various different sites. An approximate list in order of likelihood, with CDC 1996 data on frequency, is: urinary tract infections (34% in 1996), surgical site infections (17%), respiratory infections especially nosocomial pneumonia (13%), blood infections/bacteremia (14%), skin (especially burns), gastrointestinal tract infections, and central nervous system infections.

Like any infectious condition, nosocomial infections can be bacterial, viral, fungal, or even parasitic. The most common pathogens include staphylococci (especially staphylococcus aureus), pseudomonas, and Escherichia coli. However, various newer pathogens are becoming more important. Fungal conditions, mainly from candida, comprise approximately 9% of nosocomial infections.

Fungal nosocomial infections: Several fungi have become more common in nosocomial infections with a rate reported as 3.8 per 1,000 hospital patients (CDC/NNIS). The most common are Candida (mostly Candida albicans), Aspergillus, Fusarium, Trichosporon, and Malassezia. Candidiasis remains the most common type of nosocomial fungal infection, particularly in the immunocompromised. Risk factors for fungal infections include antibiotic treatments, chemotherapy, intravascular catheters, neutropenia, hemodialysis, or prior fungal infection.

Antibiotic resistance: Many of the pathogens that cause nosocomial infections have a high level of resistance to antibiotic treatments. These emerging pathogens are the most serious concerns, because they are more difficult to treat. Some of the major concerns are methicillin resistant staphylococcus aureus (MRSA), vancomycin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci (VRE).

Nosocomial Urinary tract infections: Urinary tract infections are the most common nosocomial infections. These infections can be caused by various pathogens such as E. coli, Pseudomonas, or Enterococcus.

Nosocomial pneumonia: Pneumonia is a common and serious nosocomial infection in the USA. Pneumonia is the second most common nosocomial infection in the United States. Most patients affected are have risk factors such as: mechanical ventilation (high risk), elderly, neonates, severe underlying disease, immunodeficiency, depressed sensorium, cardiopulmonary disease, or recent thoraco-abdominal surgery. Several types of pathogens can infect the respiratory tract and cause nosocomial pneumonia: bacterial pneumonia, Legionnaires' disease, pulmonary aspergillosis, Mycobacterium tuberculosis, and viral pneumonias such as Respiratory Syncytial Virus (RSV) and influenza.

Prevention of nosocomial infections: There are numerous preventive measures ranging from the obvious to high-tech. The goals are to avoid transmission by hand, by air, and by blood. Handwashing by medical staff is the single greatest improvement, but sadly this hygiene action is often lacking in many staff. Other measures include avoiding hand contact, especially to the conjunctiva or nasal areas. Various sterilization measures are helpful ranging from simple acts like sterilizing ventilators to full scale air filtering systems in the hospital. In some cases it may be appropriate to vaccinate certain patients against particular pathogens. There are numerous measures possible to avoid transmission of nosocomial infections, and the above is a brief and incomplete discussion.

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