Hospital-Acquired Infection Rate (HAI)
Last updated: Sep 12, 2025
What is Hospital-Acquired Infection Rate?
The Hospital-Acquired Infection (HAI) rate is a critical metric for measuring patient safety and the quality of care within a healthcare facility. An HAI is an infection a patient acquires while receiving medical care that was not present or incubating at the time of admission. These infections can manifest during a hospital stay or even after the patient is discharged. HAIs are a significant patient safety issue, contributing to increased morbidity, mortality, and financial strain on both patients and the healthcare system. They can be caused by various microorganisms, including bacteria and fungi, some of which may be resistant to common antibiotics.
Hospital-Acquired Infection Rate Formula
How to calculate Hospital-Acquired Infection Rate
Consider a small hospital that wants to calculate its overall HAI rate for a single month. - Total Number of Patients at Risk: 1,200 - Total Number of Diagnosed HAIs: 15 Using the simple formula: HAI Rate = 15 / 1,200 X 100 = 1.25% This means that during that month, 1.25% of patients in the hospital acquired an infection. For a more accurate, risk-adjusted calculation, the hospital would use the Standardized Infection Ratio (SIR), which is the primary summary measure for tracking HAIs in the U.S.. The SIR compares the number of infections a hospital actually observed to the number of infections that were predicted to occur based on a national average and other risk factors. - Observed Infections: 15 - Predicted Infections (based on patient mix and national data): 20 Using the SIR formula: Standardized Infection Ratio = 15 / 20 = 0.75 In this case, the hospital's SIR of 0.75 is below the national baseline of 1.0, indicating that it had fewer infections than predicted, suggesting better-than-average performance in preventing HAIs.
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What is a good Hospital-Acquired Infection Rate benchmark?
Global benchmarks for HAIs vary significantly. The World Health Organization (WHO) reports that HAI rates range from 3.6% to 12% in high-income countries, but can be as high as 19.1% in low- and middle-income countries. In Canada, a 2017 survey estimated the prevalence of patients with at least one HAI to be 7.9%. In the United States, the average rate of HAIs is approximately 6.6%. However, many health organizations now track specific types of infections, such as CLABSIs and surgical site infections, with progress reports showing national decreases in recent years.
More about Hospital-Acquired Infection Rate
HAIs represent a major challenge in healthcare globally. They are considered one of the most common adverse events in healthcare and a key indicator of patient safety. The prevalence of HAIs is a serious concern, with estimates suggesting that in Canada, one in nine hospital patients contracts an HAI. In the U.S., on any given day, about one in 31 hospital patients has at least one HAI. The financial burden is also substantial, with HAIs costing healthcare systems billions of dollars annually.
HAIs can occur in any healthcare setting, including hospitals, long-term care facilities, and outpatient clinics. The risk of acquiring an infection is heightened by factors such as a patient's weakened immune system, prolonged hospital stays, surgical procedures, and the use of invasive medical devices like catheters and ventilators. The transmission of microorganisms can happen through direct or indirect contact with contaminated equipment, healthcare personnel, or other patients.
Common types of HAIs include:
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Urinary Tract Infections (UTIs): Often associated with the use of urinary catheters.
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Surgical Site Infections (SSIs): Infections that occur at the site of a surgical incision.
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Pneumonia: A lung infection that can be a result of weakened breathing muscles from being bedridden or from the use of ventilators.
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Bloodstream Infections (BSIs): Infections that can be caused by the use of central lines or intravenous (IV) catheters.
Prevention and Best Practices
A significant portion of HAIs, estimated at 30% to 50%, are preventable. Effective infection prevention and control programs are crucial for reducing these rates. Best practices include:
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Hand Hygiene: Consistent and proper hand washing or use of alcohol-based hand sanitizers by all staff and patients is the most important measure to prevent the spread of infection.
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Sterile Techniques: Following strict sterile procedures when performing surgeries or inserting medical devices like catheters and IV lines can significantly reduce the risk of infection.
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Environmental Cleaning: Regularly cleaning and disinfecting the healthcare environment and equipment is vital to prevent transmission.
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Antibiotic Stewardship: Limiting the use of antibiotics to only when they are truly needed helps prevent the development of resistant bacteria. This is particularly important as antibiotic resistance is a growing concern that complicates the treatment of HAIs.
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Patient Education: Educating patients on how to help prevent infections, such as by maintaining personal hygiene and notifying staff about any signs of infection, is an important part of prevention.
Challenges and Insights
A key challenge in measuring HAIs is that many infections do not show symptoms until days after the patient has been discharged from the hospital, which can lead to underreporting. Another challenge is that a simple, unadjusted rate can be misleading. A hospital that treats a higher proportion of severely ill or immune-compromised patients may have a higher HAI rate even if it provides excellent care.
To address this, many health organizations, such as the Centers for Disease Control and Prevention (CDC) in the U.S., use a Standardized Infection Ratio (SIR). The SIR is a risk-adjusted metric that compares the number of infections a hospital actually observed to the number of infections that were predicted to occur based on national data and risk factors like patient demographics and the type of hospital unit. An SIR of 1.0 represents the national baseline, so an SIR less than 1.0 is considered better, as it indicates fewer infections than predicted.
Hospital-Acquired Infection Rate Frequently Asked Questions
Can a patient be readmitted to a hospital for an HAI that they developed during their first stay?
Yes. An HAI is defined as an infection acquired during healthcare delivery that was not present or incubating at the time of admission. It is possible for a patient to develop an infection in the hospital and be discharged before symptoms appear, leading to readmission for the same infection later.
How do hospitals track HAIs?
Hospitals use various surveillance methods to track HAIs, including manual data collection and computerised surveillance systems. The data collected includes the number of cases and the population at risk, which is often measured in patient days or device days for device-related infections.
Are certain patient populations at a higher risk of HAIs?
Yes. Patients who are more susceptible to HAIs include infants, the elderly, those with weakened immune systems, and people with conditions like diabetes or multiple illnesses. Patients who have undergone surgical procedures or have invasive medical devices are also at a higher risk.