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Hospital Size Strongly Associated with Higher Infection Rates, to a Point

Though hospitals have successfully reduced the rate of hospital-acquired conditions (HACs) since the introduction of the ACA and associated penalty programs, progress has slowed in recent years and some infection rates have increased. Nearly 250,000 patients experience one or more HACs each year, and the CDC estimates about 23,000 cases prove fatal. Given the scope of the problem, it could be useful to identify the types of hospitals that have the most trouble preventing and controlling hospital-associated infections (HAIs). According to an analysis of Definitive Healthcare data, higher infection rates are generally associated with larger hospital size and a few other clinical factors, but the trend is reversed among the worst performers.

Most hospitals report HAIs through CMS’ HAC Reduction Program, which penalizes hospitals in the 75th percentile or higher for infections and other preventable patient injuries. For infection measures of the program, hospitals are graded by the standardized infection ratio (SIR), which compares a hospital’s actual number of cases to a predicted volume that adjusts for risk and other factors. A ratio of one indicates that the hospital experienced the predicted number of infection cases, with excessive cases creating a ratio over one and vice versa.

The SIR is designed so a wide variety of hospitals can be compared, but the data show that many of the factors accounted for in the risk-adjustment still correlate with worse infection rates. The greatest example is facility size, as a hospital with more staffed beds will be more likely to facilitate the spread of infectious diseases between patients. When grouping hospital SIRs into quartiles for each infection measure, the third quartile consistently has the highest number of discharges and staffed beds, while the second has more than the first, as seen in the chart below. Given that the trend is visible in all types of HAIs examined, it seems likely that the current adjustment for hospital size is not strong enough, especially as existing research has also suggested a link between patient volume and HAI prevalence. However, other explanations could include inadequate staffing at larger hospitals or another factor not included in the available data.

HAI Quartile


The trend can be found in other factors, though not as strongly. Of these, case mix is the most prominent, and the analysis is consistent with existing studies and research that have found a significant correlation between case mix and worse HAC Reduction Program scores.  A higher case mix is associated with a worse SIR for some measures but not others. The median case mix difference for C Diff between the first and third quartiles 0.22, while that for MRSA is 0.05. However, for MRSA, the case mix for the fourth quartile is lower than that of the first, contrary to the trend. The reason for the discrepancy is not immediately clear, and would require a stronger analysis of the connection between case mix and individual infections. Other weaker correlations include the rate of existing complicating conditions and the Medicaid payer mix, which vary only by a few percentage points among quartiles.

The fact that the median fourth-quartile hospital is smaller and has a lower case mix than other facilities with superior performance is counter-intuitive, but not surprising. Infection control is a difficult process that often requires a time-consuming and thorough decontamination of rooms, equipment, and often any hospital area frequented by patients. Providers, too, must adhere to strict infection control protocols to limit HAIs. If the hospitals in the fourth quartile fail in this regard, then the smaller size may be less significant of a positive factor, compared to a larger facility with a stronger program. It’s also possible that the smaller size of the fourth-quartile hospitals indicates a relative shortage of resources or providers, which could contribute to a higher infection rate.

Some observers have portrayed the future of infection control as somewhat bleak, given the growth of antibiotic-resistant bacteria. In addition, an outbreak of MRSA at a California hospital in early 2017 despite adherence to a widely accepted infection control protocol has reignited the debate over the best methods of preventing HAIs. However, the data suggests that a significant number of hospitals still have room to improve, even if the decline in HAIs at most facilities has stalled. Existing drugs and protocols can still serve these hospitals well if properly exercised.

Definitive Healthcare has the most up-to-date, comprehensive and integrated data on over 7,700 hospitals, 1.4 million physicians, and numerous other healthcare providers. Our facility profiles include detailed current and historical financial information for hospitals, health systems, skilled nursing facilities, and more.

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