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
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
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
- intrinsic contamination, i.e., contamination of the device or
solution at the time of manufacture;
- extrinsic contamination, i.e., contamination of the device or
solution after manufacture but before insertion or infusion into
- 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
- 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
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.
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:
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Last update on: 10/2/2006