87 HOSPITAL-ACQUIRED INFECTIONS
Harrison’s Manual of Medicine
Clinical Manifestations and Diagnosis
Hospital Infection Control
Nosocomial infections are acquired during or as a result of hospitalization and generally manifest after 48 h of hospitalization.
It is estimated that 5% of pts admitted to an acute-care hospital in the U.S. acquire a new infection; this estimate translates into about 2 million nosocomial infections per year, with an annual cost >$2 billion. The most common types of hospital-acquired infections are UTI, surgical wound infection, and pneumonia. Primary bacteremias, especially those associated with intravascular devices, have increased in frequency, as have infections in ICUs and those caused by antimicrobial-resistant pathogens.
Risk factors for the development of UTI include female sex, prolonged urinary catheterization, absence of systemic antibiotics, and inappropriate catheter care. Risk factors for surgical wound infection include presence of a drain, longer preoperative hospital stay, preoperative shaving of the field, longer duration of surgery, presence of an untreated remote infection, and higher-risk surgeon. An index for assessing the risk of wound infection has been developed, with risk factors including abdominal surgery, surgery lasting >2 h, contaminated or dirty-infected surgery (according to the classic classification system), and three or more diagnoses for one pt.
Risk factors for pneumonia include ICU stay, intubation, altered level of consciousness (esp. with a nasogastric tube in place), old age, chronic lung disease, prior surgery, and use of H2 blockers or antacids. There are conflicting data on whether sucralfate (a medication that heals ulcers without altering gastric pH) decreases the risk of pneumonia in intubated pts. The major risk factors for the development of primary bacteremia are the presence of an indwelling intravascular device and hyperalimentation.
Clinical Manifestations and Diagnosis
DIFFERENTIAL DIAGNOSIS OF FEVER Other important infectious sources of new fever in a hospitalized pt include antibiotic-associated diarrhea usually caused by Clostridium difficile, decubitus ulcers, and sinusitis. Noninfectious sources of fever to consider include drugs (drug fever may occur with or without eosinophilia or rash), thrombophlebitis, pulmonary embolism, hematoma, pancreatitis, atelectasis, and acalculous cholecystitis.
WORKUP FOR NEW FEVER The workup of a hospitalized pt with new fever should include a thorough history directed at symptoms such as headache, cough, abdominal pain, diarrhea, flank pain, dysuria, urinary frequency, and leg pain. Features of the hospitalization, such as the presence of IV devices, use of a urinary catheter, performance of surgical procedures, and use of new medications, are all important items. The physical exam should pay particular attention to skin, lungs, abdomen (esp. the RUQ), costovertebral angles, surgical wounds, calves, and current or old IV sites. Laboratory tests for all febrile hospitalized pts should include CBC with differential, CXR, and blood and urine cultures. Other diagnostic tests to consider include LFTs; abdominal studies; routine aerobic cultures of sputum, stool, or other relevant body fluids; and testing of stool for C. difficile toxin in cases of diarrhea.
URINARY TRACT INFECTION Fever, dysuria, frequency, leukocytosis, and flank pain or costovertebral angle tenderness correlate well with bladder infection or pyelonephritis in pts who have had urinary catheters in place. In pts with fever alone, the finding of WBCs without epithelial cells in the urinary sediment or the detection of leukocyte esterase or nitrite on urinalysis is suggestive of UTI. A urine culture positive for a single organism in an asymptomatic hospitalized pt is not diagnostic of UTI.
SURGICAL WOUND INFECTION Erythema extending >2 cm beyond the margin of the wound, localized tenderness and induration, fluctuance, drainage of purulent material, and dehiscence of sutures are all findings suggestive of a wound infection. In pts with sternal wounds, ongoing fever or the development of rocking or instability of the sternum may indicate the need for surgical exploration of the wound.
PNEUMONIA In pts outside the ICU, pneumonia should be suspected in the setting of a new infiltrate on CXR, a new cough, fever, leukocytosis, and sputum production. In pts receiving intensive care, esp. those who are intubated, signs may be more subtle; purulent sputum and abnormal CXRs are common. A change in character or quantity of sputum in an intubated pt with fever, with or without accompanying CXR changes, is significant. Organisms of concern in nosocomial pneumonia are gram-negative aerobic bacilli—particularly Pseudomonas aeruginosa, Klebsiella pneumoniae, and Enterobacter spp.—and Staphylococcus aureus. Viruses such as respiratory syncytial virus and adenovirus are also important. Depending on the institution, pathogens such as methicillin-resistant S. aureus, Stenotrophomonas maltophilia, Flavobacterium spp., and even Legionella spp. may be of special concern.
BACTEREMIA AND INTRAVASCULAR DEVICE–RELATED INFECTION The only presenting symptom may be fever. The exit site of an existing or previous IV line should be evaluated for erythema, induration, tenderness, and/or purulent drainage. Organisms of particular concern include coagulase-negative staphylococci, Candida spp., S. aureus, and enterococci.
Therapy should be directed at the most likely cause of infection and, when possible, should be chosen on the basis of culture results. To reduce the rate of development of antibiotic-resistant infections, antibiotic courses should be kept as short as possible, with coverage as narrow as possible for the organism(s) involved. When an infection is known to be related to an intravascular device or when no other source of infection is apparent, the device should usually be removed and the catheter tip sent for quantitative culture. Whenever feasible, a new intravascular device should be inserted at a different site. Use of antiseptic- or antibiotic-impregnated devices should be considered.
Hospital Infection Control
Infection control departments determine the general and specific measures used to control infections. Cross-infection is particularly important, and hand washing is the single most important preventive measure in hospitals. Minimizing invasive procedures and vascular and bladder catheterizations to those that are absolutely necessary will also reduce rates of nosocomial infection. Standard precautions are designed for the care of all pts to reduce the risk of infection from both recognized and unrecognized sources. These precautions include the use of hand washing and gloves for all potential contacts with blood, body fluids, and mucous membranes. In some cases gowns, masks, and eye protection are also indicated. Three more specific sets of precautions are based on probable routes of transmission: droplet precautions (e.g., for untreated meningitis), airborne precautions (e.g., for suspected tuberculosis, with fulfillment of specific ventilation requirements), and contact precautions (e.g., for C. difficile diarrhea). Sets of precautions may be combined for diseases that have more than one route of transmission (e.g., varicella).
For a more detailed discussion, see Zaleznik DF: Hospital-Acquired and Intravascular Device–Related Infections, Chap. 135, p. 857; and Weinstein RA: Infection Control in the Hospital, Chap. 134, p. 853, in HPIM-15.