Types of Hospital Acquired Infections

Since the late 1950’s the study and attempted control of hospital acquired (nosocomial) infections has been shaped by the discipline of public health, with its emphasis on surveillance and epidemiologic methods.¹ Hospital acquired infections are not only the most common type of adverse event in healthcare, they may also be the most studied. Accordingly, infection control is unquestionably a critical component of patient safety.

Transmission of infection within a hospital requires three elements: (1) a source of infecting microorganisms, (2) a susceptible host, and (3) a means of transmission for the microorganism.²

There are four general types of infection which account for more than 80 percent of all hospital acquired infections ³:

• urinary tract infection, usually catheter-associated;
• surgical-site infection;
• bloodstream infection, usually associated with the use of an intravascular device; and,
• pneumonia, which is usually ventilator-associated.

One quarter of all nosocomial infections involve patients in intensive care units, and most patients who die in ICU’s die of infection(s). ⁴ Seventy percent of hospital acquired infections are due to microorganisms that are resistant to one or more antibiotics. This emerging public health crisis is due in large part to indiscriminate use of antibiotics by physicians. ⁵

Nosocomial infections are also ranked according to their frequencies, associated mortality rates, costs, or relative changes in frequency over recent years. ⁶ For instance:

• Catheter-associated urinary tract infections are the most frequent (accounting for about 35 percent of nosocomial infection) but carry the lowest mortality and lowest cost.
• Surgical-site infections are second in frequency (about 20 percent) and third in costs.
• Bloodstream infections and pneumonia are less common (about 15 percent each) but are associated with much higher mortality and costs.

Blood stream infections and methicillin-resistant Staphylococcus aureus infections share notoriety for being both the highest-cost infections and the most rapidly increasing in frequency. The current incidence of blood stream infections is nearly three times the incidence in 1975. ⁷ (see, Understanding the Costs of Medical Errors).

Urinary Tract Infection (UTI).
The healthy urinary bladder is sterile, which means it doesn't have any bacteria or other microorganisms in it. There may be bacteria in or around the urethra but they normally cannot enter the bladder. Catheterization is the placement of a catheter through the urethra into the bladder. Most hospital-acquired UTIs happen after urinary catheterization. ⁸

Many of the infecting microorganisms are part of the patient's endogenous bowel flora, but can also be acquired by cross-contamination from other patients or hospital personnel or by exposure to contaminated solutions or non-sterile equipment. ⁹

Urinary catheters should be inserted only when necessary and left in place only for as long as necessary. They should not be used solely for the convenience of patient-care personnel. ¹⁰

Surgical-site Infections (SSIs).
SSIs are divided into incisional and organ space. Incisional SSIs are further classified as superficial-incisional (involving the skin and subcutaneous tissues) or deep-incisional (involving deep soft tissues). Two-thirds of SSIs are confined to the incision, and one-third involve the organ or space accessed during surgery. ¹¹

An organ/space SSI involves any part of the body, excluding the skin incision, fascia, or muscle layers, that is opened or manipulated during the operative procedure. One example would be Osteomyelitis, a bone infection. ¹² The term cure is not used in osteomyelitis, since the bone infection may recur years after apparently successful treatment of the disease. ¹³

Incorrect timing of surgical prophylaxis is associated with increases by a factor of two to six in the rates of surgical-site infection.¹⁴ Failure to administer the first dose of antibiotic within 60 minutes before surgical incision remains a common error, due in part to prior studies that suggested a larger window period. Additionally, prophylactic antimicrobials should be discontinued within 24 hours after the end of surgery.¹⁵

Bloodstream Infections (BSIs).
Nosocomial bloodstream infections (BSIs) have been divided into two categories. Primary bloodstream infections occur without any recognizable focus of infection with the same organism at another anatomic site at the time of positive blood culture. Episodes of bloodstream infections secondary to intravenous or arterial lines are typically classified as primary bacterium. Secondary bloodstream infections are infections that developed subsequent to a documented infection with the same microorganism at another body site. ¹⁶

The prevalence of primary BSIs and the pathogens causing these infections are highly correlated with the frequency of use of intravascular catheters. The microorganism may be introduced into the bloodstream by ¹⁷:

1. intrinsic contamination, i.e., contamination of the device or solution at the time of manufacture;
2. extrinsic contamination, i.e., contamination of the device or solution after manufacture but before insertion or infusion into the patient;
3. contamination of the catheter after insertion, i.e., via the hands of healthcare workers (HCWs) during manipulation of catheter, catheter site, or fluid pathway; or
4. egress of patient's own skin flora along the catheter track.

Intrinsic contamination of medical devices or infusates has become nearly unheard of in the United States and throughout the developed work as sterility assurance procedures have been standardized and fully implemented by most manufactures. ¹⁸

Pneumonia.
Bacteria and other microorganisms are easily brought into the throat by respiratory procedures commonly done in the hospital. The microorganisms come from contaminated equipment or the hands of healthcare workers. Some of these procedures are respiratory intubation, suctioning of material from the throat and mouth, and mechanical ventilation. Once the throat is colonized, it is easy for the patient to inhale the microorganism into the lungs. The inhaled microorganisms grow in the lungs and cause an infection that can lead to pneumonia. ¹⁹

Unfortunately, hospitals are not required to report death and infection rate data to any state or federal agency. Moreover, no data is publicly available for consumers in the vast majority of states. Only Illinois, Pennsylvania, Missouri, and Florida mandate reporting requirements with disclosure to the public.

Consumers Union’s recent StopHospitalInfections.org project is working to enact public disclosure laws so that consumers can select the safest hospitals and competition among hospitals will force the worst to improve. More information about hospital acquired infections and Consumers Union’s campaign can be found at: www.StopHospitalInfections.org.

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Last update on: 10/2/2006

1. Burke J. Infection Control – A Problem for Patient Safety. The New England Journal of Medicine. 2000; 348:7.
2. Bennett JV, Brachman PS. Hospital Infections Lippincott-Raven 1998
3. Burke J. Infection Control – A Problem for Patient Safety. The New England Journal of Medicine. 2000; 348:651.
4. Rello J. Impact of Nosocomial Infections on Outcome: Myths and Evidence. Infect Control Hosp Epidemiol. 1999; 20:392.
5. Eggimann P, Pittet D. Infection Control in the ICU. Chest 2001; 120:2059.
6. Burke J. Infection Control – A Problem for Patient Safety. The New England Journal of Medicine. 2000; 348:651.
7. Ibid.
8. MyDiseasesDex, Micromedex, Inc. 1999-2001.
9. Wong ES. Guideline for Prevention of Catheter-associated Urinary Tract Infections, Center for Disease Control, U.S. Department of Health & Human Services. 1981.
10. Ibid.
11. Wenzel RP. Prevention and Control of Nosocomial Infections. Lippincott Williams & Wilkins. 2003
12. Olmsted RN. APIC Infection Control and Applied Epidemiology: Principles and Practices. St. Louis: Mosby; 1996 (Reprinted from: Garner JS, Jarvis WR, Emori TG, Horan TC, Hughes JM, CDC Definitions for Nosocomial Infections).
13. Mandell GL, Bennett JE, Dolin R. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases 2000.
14. Burke J. Infection Control – A Problem for Patient Safety. The New England Journal of Medicine. 2003; 348:651.
15. Bratzler DW, Houck PM. Antimicrobial Prophylaxis for Surgery: An Advisory Statement from the National Surgical Infection Prevention Project. Clinical Infectious Diseases. 2004; 38: 1706.
16. Wenzel RP. Prevention and Control of Nosocomial Infections. Williams and Wilkinson. 1993.
17. Jarvis WR, Cookson ST, Robles MB. Prevention of Nosocomial Bloodstream Infections: A National and International Priority. Infect Control Hosp Epidemiol 1996; 17:272.
18. Ibid.
19. MyDiseasesDex, Micromedex, Inc. 1999-2001.