What Are Hospital Acquired Infections?

Hospital-acquired infections, also known as “healthcare-associated infections” or “nosocomial infection,” refer to infections that were not present before seeking medical care and were acquired in a healthcare setting. Hospital-acquired infections can be contracted in hospitals even in the intensive care unit, ambulatory clinics, surgical centers, nursing homes, long-term care facilities, dialysis centers, and diagnostic laboratories. 

Hospital-acquired infections are defined by symptoms presenting 48-or-more hours after hospital admission, within three days of discharge, or 30 days postoperatively (1). The vast majority of hospital-acquired infections are caused by bacteria, and the propagation of these infections is worsened by the increasing presence of multi-drug resistant bacterial strains.

Prevalence of Hospital-Acquired Infections

In the United States, approximately 1 in 25 hospitalized patients will contract an infection (2). Data collected by the Centers for Disease Control and Prevention identified an estimated 1.7 million hospital-acquired infections in the United States during 2002, resulting in 99,000 associated deaths (3).

Estimates from the UK place the prevalence of hospital-acquired infections at approximately 1-in-10 patients (1). In developing nations, the prevalence is higher and may occasionally exceed 25% (4).

CDC data show that urinary tract infections make up approximately 36% of all hospital-acquired infections in the ICU, surgical site infections 20%, pneumonia 11%, bloodstream infections 11%, and other infections 22% (3).

Risk Factors

Immunocompromised individuals, such as those undergoing chemotherapy, are at an increased risk for hospital-acquired infection. Geriatric patients are also at increased risk, as are those with multiple medical comorbidities. The incidence of hospital-acquired infections increases as the length of hospital stay increases. Patients in the ICU, receiving mechanical ventilator support, undergoing surgery, and having indwelling devices are also at increased risk.

One large study that examined 231,459 patients across 947 hospitals in Europe found that 19.5% of patients in the ICU experienced at least one hospital-acquired infection (5).

Catheter-Associated Urinary Tract Infections (CAUTI)

Catheter-associated urinary tract infections are the most common forms of hospital-acquired infection. Approximately 75% of all UTIs contracted in the hospital are associated with catheter use, and the most important risk factor for developing a catheter-associated urinary tract infection is prolonged catheter use (6). Common pathogens identified in catheter-associated urinary tract infections include Escherichia coli, Enterococcus species, Staphylococcus aureus, Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, Morganella morganii, and Candida albicans. Some organisms, including Pseudomonas and Proteus, can form biofilms around catheters.

Surgical Site Infections (SSI)

Surgical site infections occur postoperatively in the skin, internal organs, or implanted materials involved in the surgery. Diabetic patients are at an increased risk of developing surgical site infections. The incidence of surgical site infections increases as procedure duration increases and the use of antimicrobial prophylaxis decreases the risk of such infections. Common causes of surgical site infections include Staphylococcus aureus (including MRSA), coagulase-negative Staphylococcus, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii. In developed nations, between 2-5% of all patients who undergo surgery develop a surgical site infection; and in developing nations, between 12%-39% do (4).

Hospital-Acquired Pneumonia (HAP) and Ventilator-Associated Pneumonia (VAP)

The Infectious Diseases Society of America (IDSA) defines hospital-acquired pneumonia as “pneumonia that occurs 48 hours or more after admission to the hospital and did not appear to be incubating at the time of admission”; and defines ventilator-associated pneumonia as “pneumonia that develops more than 48 to 72 hours after endotracheal intubation.” Common bacterial causes of both hospital-acquired pneumonia and ventilator-associated pneumonia include Staphylococcus aureus (including MRSA), Streptococcus pneumoniae, Haemophilus influenzae, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Common viral causes include rhinovirus, parainfluenza virus, influenza virus, respiratory syncytial virus, and coronavirus. 

The incidence of ventilator-associated pneumonia in patients who require mechanical ventilation for more than 48 hours is estimated at 25-to-30% (7).

Central Line-Associated Bloodstream Infection (CLABSI)

Central line-associated bloodstream infections occur at the site of central venous catheters. The mortality rate for central line-associated bloodstream infections is between 12% and 25% (8). Common causes of central line-associated bloodstream infections include coagulase-negative Staphylococci, Staphylococcus aureus (including MRSA), Enterobacte, Klebsiella pneumoniae, and Candida albicans. Central lines can be placed in the neck, chest, arm, or groin. The use of femoral-site lines is associated with an increased risk of infection and is no longer recommended (9). Antibiotic lock therapy can reduce the incidence of central line-associated bloodstream infections.

Clostridium Difficile Infections (CDI)

An estimated 12.1% of all hospital-acquired infections are caused by Clostridium difficile, making Clostridium difficile the most common cause of hospital-acquired infections (10). Approximately 75% of all Clostridium difficile infections are hospital-acquired (11), and an estimated 2.3% of all US hospital costs are related to these infections (12).

Hospital-Acquired COVID-19

The incidence of hospital-acquired COVID-19 remains unknown. A meta-analysis of studies examining COVID-19 cases in China found that 44% of cases were likely to have originated from a healthcare setting (13). A hospital in South Africa reported that a single case led to six major outbreak clusters in several hospital wards, a nursing home, and a dialysis unit. Ultimately this episode resulted in 135 infections and 15 deaths (14). Up to 1-in-4 cases of COVID-19 in the UK are likely to have been hospital-acquired (15).

In contrast, a recent study from the United States suggests that hospital-acquired COVID-19 is actually quite uncommon when rigorous infection-control measures are followed. This study looked at all patients admitted to Brigham and Women’s Hospital in Boston, Massachusetts, between March 7 and May 30, 2020. They determined that of 697 COVID-19 diagnoses, only two were hospital-acquired, including one case that likely resulted from a visit by a pre-symptomatic spouse (16).

The World Health Organization estimates that healthcare workers may comprise as many as one-in-seven COVID-19 cases (17), reflecting a high incidence of hospital-acquired disease. The CDC is not currently collecting data on hospital-acquired COVID-19, as hospitals are required to report to the U.S. Department of Health and Human Services. 

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References 

(1) Inweregbu, K., Dave, J. and Pittard, A., 2005. Nosocomial infections. Continuing Education in Anaesthesia Critical Care & Pain, 5(1), pp.14-17.

(2) Magill SS, Edwards JR, Bamberg W, et al., 2014. Emerging Infections Program Healthcare-Associated Infections and Antimicrobial Use Prevalence Survey Team. Multistate point-prevalence survey of healthcare-associated infections. N Engl J Med, 27;370(13), pp. 1198-208.

(3) Klevens, R., Edwards, J., Richards, C., et al., 2007. Estimating Health Care-Associated Infections and Deaths in U.S. Hospitals, 2002. Public Health Reports, 122(2), pp.160-166.

(4) Allegranzi, B. and Pittet, D., 2007. Healthcare-Associated Infection in Developing Countries: Simple Solutions to Meet Complex Challenges. Infection Control & Hospital Epidemiology, 28(12), pp.1323-1327. 

(5) European Centre for Disease Prevention and Control, 2013. Point-prevalence survey of healthcare-associated infections and antimicrobial use in European acute care hospitals. Stockholm: EDC.

(6) Cdc.gov. 2021. Catheter-associated Urinary Tract Infections (CAUTI) | HAI | CDC. [online] 

(7) Cornejo-Juárez, P., González-Oros, I., Mota-Castañeda, P., Vilar-Compte, D. and Volkow-Fernández, P., 2020. Ventilator-associated pneumonia in patients with cancer: Impact of multidrug resistant bacteria. World Journal of Critical Care Medicine, 9(3), pp.43-53.

(8) Dumont, C. and Nesselrodt, D., 2012. Preventing central line-associated bloodstream infections CLABSI. Nursing, 42(6), pp.41-46. 

(9) Palmer, E., 2021. Avoiding the femoral vein in central venous cannulation: an outdated practice. [online] Acphospitalist.org. 

(10) Monegro, A., Muppidi, V. and Regunath, H., 2020. Hospital Acquired Infections. StatPearls, [online]

(11) Louh, I., Greendyke, W., Hermann, E., e al., 2017. Clostridium Difficile Infection in Acute Care Hospitals: Systematic Review and Best Practices for Prevention. Infection Control & Hospital Epidemiology, 38(4), pp.476-482.

(12) Jump, R., 2013. Clostridium difficile infection in older adults. Aging health, 9(4), pp.403-414.

(13) Zhou, Q., Gao, Y., Wang, X., et al., 2020. Nosocomial infections among patients with COVID-19, SARS, and MERS: a rapid review and meta-analysis. Annals of Translational Medicine, 8(10), pp.629-629.

(14) Lessells, R., Moosa, Y., and de Oliviera, T., 2020. Report into a nosocomial outbreak of coronavirus disease 2019 (COVID‐19) at Netcare St. Augustine’s Hospital. [online]

(15) Discombe, M., 2021. Covid infections caught in hospital rise by a third in one week. [online] Health Service Journal. 

(16) Rhee, C., Baker, M., Vaidya, V., et al., 2020. Incidence of Nosocomial COVID-19 in Patients Hospitalized at a Large US Academic Medical Center. JAMA Network Open, 3(9), p.e2020498.

(17) Nebehay, S., 2021. One in 7 reported COVID-19 infections is among health workers, WHO says. [online] U.S.