Readmissions for Selected Infections Due to Medical Care: Expanding the Definition of a Patient Safety Indicator

Introduction

Awareness by researchers and health policymakers of medical errors and their consequences has been heightened since the publication of the Institute of Medicine's (IOM) report, To Err Is Human: Building a Safer Health System. ¹ The Agency for Healthcare Research and Quality (AHRQ) has accelerated efforts to address the problems raised by this report by improving the identification of medical errors. As a part of its response, AHRQ has developed a set of quality indicators designed to evaluate health care delivered in inpatient and ambulatory care settings. Complications of care and adverse events occurring in the inpatient hospital setting that may be related to quality of care problems are captured by AHRQ's Patient Safety Indicators (PSIs).^{2, 3}

The PSIs are a set of measures that identify problems that patients experience as a result of contact with the health care system—problems that are likely preventable by changes at the system or provider level.⁴ The PSIs have been defined using only the type of information found in inpatient hospital discharge abstract data; the specific data elements required by the PSI algorithms are available from most hospital and State-level inpatient administrative data systems. PSIs are defined at the hospital level and the area level:

• Hospital-level indicators identify potentially preventable complications that arose while patients were hospitalized for their initial care. Secondary diagnosis codes (condition not present at admission) are used to identify patients with the hospital-level indicators.

• Area-level indicators identify all cases of the potentially preventable complications that occur in a given geographic area (e.g., metropolitan service area or county); they include complications that arose during hospitalization or that resulted in a subsequent hospitalization. The principal diagnosis (condition present at admission), as well as secondary diagnoses, are used to define the area-level indicators. The area-level definition adds cases where a patient's risk of the complication occurred in a separate encounter with the health care system (inpatient or outpatient).

AHRQ developed the hospital-level PSIs to capture inpatient events that occur during a single admission, recognizing that many State administrative databases do not have the capability of tracking patients across multiple admissions. One flaw in using is the possibility of underestimating the prevalence of some of the PSIs attributable to inpatient care: adverse events that occur shortly after discharge and result in readmission are not captured in hospital-level PSIs. This study uses only data from a New York hospital discharge administrative database, which is capable of tracking patients across multiple admissions. These data help estimate the volume of those adverse events that occur in the admission during which an intravascular device is inserted, but are not captured when reporting only the hospital-level PSI Selected Infections Due to Medical Care. By attributing area-level PSI cases that occur because of inpatient care to the hospital-level PSI, the sensitivity of the hospital-level PSI can be increased. This study also examines the characteristics of these readmitted patients relative to patients who suffer from Selected Infections Due to Medical Care in the initial admission. Finally, we examine the number of cases and characteristics of patients captured by the hospital-level and the area-level PSI, and the resulting readmissions to evaluate the relative contribution of events from various health care settings.

Methods

Results

Table 1

Numbers and rates of AHRQ Infection Due to Medical (more...)

Table 1

Numbers and rates of AHRQ Infection Due to Medical Care cases and patients readmitted within 30 days, among New York discharges, 2001

	N	Rate (%)
Total discharges	2,478,204	-
Eligible hospital-level risk pool	1,908,568	77.0
AHRQ Infection Due to Medical Care cases (hospital)	3,858	0.202
Total readmissions within 30 days (all causes)	425,359
Readmissions within 30 days with primary diagnosis of Infection Due to Medical Care	950	0.050
Eligible area-level risk pool	19,011,378	-
AHRQ Infection Due to Medical Care cases (area)	7,373	0.0387

Table 2

Comparison of renal dialysis patients among hospital-level (more...)

Table 2

Comparison of renal dialysis patients among hospital-level PSI patients, area-level PSI patients, and readmitted patients

	Renal dialysis			No renal dialysis
	N	n	%	n	%
Hospital-level PSI patients	3,858	990	25.7	2,868	74.3
Readmits*	950	528	55.6	422	44.4
Outpatients**	2,611	1,690	64.7	921	35.3

* Readmits: cases readmitted to the hospital with a principal diagnosis of Selected Infection Due to Medical Care within 30 days of a prior hospitalization.

** Outpatients: cases meeting the area-level criteria but not in the hospital-level PSI patients or readmits group.

Table 3

Mortality rates and morbidity for Infection Due to (more...)

Table 3

Mortality rates and morbidity for Infection Due to Medical Care patients, patients readmitted within 30 days

	Infection Due to Medical Care Patients	Patients readmitted within 30 days	Infection Due to Medical Care patients and patients readmitted within 30 days	Change with inclusion of patients readmitted within 30 days*
	(n = 8,358)	(n = 950)	(n = 4,808)
	% or median	% or median	% or median	%
Mortality	15.7	6.3	11.0	-29.9†
Cellulitis	15.0	13.2	14.1	-6.0
Septicemia	35.5	39.2	37.4	+5.2†
Bacteremia	12.0	11.8	11.9	-0.8

*

Percent change in mortality/morbidity between Infection Due to Medical Care patients and Infection Due to Medical Care patients combined with patients readmitted within 30 days

+

percent increase; - percent decrease.

†

The difference between the Infection Due to Medical Care patients and Infection Due to Medical Care patients combined with patients readmitted within 30 days groups was significant.

Table 4

Distributions of sex, race and age among Infection (more...)

Table 4

Distributions of sex, race and age among Infection Due to Medical Care patients and patients readmitted within 30 days

		Infection Due to Medical Care Patients		Patients readmitted within 30 days		Infection Due to Medical Care patients compared to patients readmitted within 30 days
		(n = 8,358)		(n = 950)
		n	%	n	%	P-value
Sex						0.6241
	Male	1842	47.7	462	48.6
	Female	2016	52.3	488	51.4
Race/Ethnicity						<0.0001
	White	2250	58.3	466	49.1
	Black	777	20.1	263	27.7
	Hispanic	299	7.8	89	9.4
	Asian/Pacific	43	1.1	20	2.1
	Native American	9	0.2	2	0.2
	Other	480	12.4	110	11.6
Age						<0.0001
	0–20	204	5.3	52	5.5
	20–30	198	5.1	54	5.7
	30–40	292	7.6	75	7.9
	40–50	432	11.2	130	13.7
	50–60	556	14.4	169	17.8
	60–70	671	17.4	193	20.3
	70–80	817	21.2	169	17.8
	80 +	688	17.8	108	11.4

Discussion

The Patient Safety Indicators, like the Complication Screening Programs and other algorithms designed to be used with hospital discharge data, are a valuable tool for measuring the potential burden associated with medical errors. The selection of events defined by the PSIs are also unique in that they all have readily available techniques to help prevent these complications. In the case of inserting an intravascular device, the appropriate technique has recently been defined to include (1) inserting intravascular device in the subclavian vein; (2) using maximum barrier protection during all intravascular device insertions; (3) using chlorhexidine-based products to clean the insertion site; and (4) using antimicrobial-treated intravascular devices in select patient groups.⁵

The focus of this study, the PSI for Selected Infections Due to Medical Care, identifies infections related to catheters and intravenous lines. Infections due to intravascular devices can lead to local site infection, catheter-related blood stream infection, septic thrombophlebitis, endocarditis, and other metastatic infections; they have been associated with increased attributable mortality.⁶ Critically ill patients are at significant risk of nosocomial bloodstream infection.^{7, 8} Most bloodstream infections are related to a primary infection, the majority of which originate from intravascular devices.⁹–¹² Intravascular device-associated bloodstream infections increase the length of stay of patients and the cost of health care.¹³–¹⁵ Patients in the intensive care unit setting are at increased risk of acquiring bloodstream infections, and it has been estimated that 80,000 intravenous device-related bloodstream infections occur annually in the intensive care unit.^{16, 17} If the entire hospital setting is examined, the estimate of intravascular device-related bloodstream infections increases to 250,000 annually.¹⁸

The methodology employed by AHRQ to define PSIs can be applied to administrative data maintained by most States. The use of ICD-9-CM diagnosis and procedure codes from administrative data to identify potential adverse events may lead to incomplete or inaccurate ascertainment of events, as acknowledged by AHRQ, but they represent a convenient and easy-to-implement method for estimating the prevalence of numerous important complications that occur during inpatient admissions.

In New York during 2001, 3,858 instances of hospital-level cases of Infection Due to Medical Care were identified. New York's rate of 2.02 per 1,000 surgical discharges is similar to recently published estimates using the AHRQ PSIs. Romano et al. established a Selected Infections Due to Medical Care rate of 1.93 per 1,000 using data from the 2000 Nationwide Inpatient Sample.¹⁹

In New York during 2001, an additional 950 patients with a principal diagnosis of Selected Infections Due to Medical Care were found among those who were readmitted to hospitals within 30 days of a previous inpatient hospital admission. The addition of 950 cases increases the hospital-level AHRQ PSI-based estimate of 3,858 cases of Selected Infections Due to Medical Care in New York State by 25 percent, and increases the rate of this complication from 2.02 per 1,000 surgical discharges to 2.52 per 1,000 surgical discharges. The cases captured by the hospital-level PSI and the readmissions represent patients who received their care in the inpatient setting and developed an infection due to medical care.

The methods used to identify readmissions involved using two match criteria. First, medical record number and hospital code were used. This is appropriate in New York SPARCS, where the medical record number for the same patient is maintained over time. Although the system generally follows this policy, there are instances where patients do not end up with the same medical record number over time. We also used the unique patient identifier in combination with the patient's date of birth. This second criteria allowed for the linkage of records for a single individual across hospitals. The results of this match process indicated that 770 patients out of 950 readmissions (81 percent) were readmitted to the same hospital. If the medical record number and hospital identification code can be used to identify all of these cases, then States that do not have a unique identifier could still capture a large portion of their readmissions with these codes alone. Analyzing our results, we found that not all of the patients who were identified as readmissions to the same hospital had the same medical record number. If we restrict the matching of patients across hospital stays to only the medical record number and hospital code, 716 patients were identified as readmissions. This represents 75 percent of the 950 patients that we were able to link using all variables. Therefore, it would seem prudent for States with a medical record number and hospital code in their discharge data to attempt to link patients across admissions. While using these variables does not capture all of the linkages possible with other variables, it nonetheless captured 75 percent of the readmissions in New York State data for Infections Due to Medical Care.

An additional finding of this analysis is that the current definition for the hospital-level PSI identifies cases that have Selected Infections Due to Medical Care diagnosis codes in the principal and secondary positions. This occurs when a patient has a secondary code for Selected Infections Due to Medical Care that meets the criteria for inclusion in the numerator of the PSI, and the patient also has a principal diagnosis of Selected Infections Due to Medical Care. Because the intent of the hospital-level indicator is to identify cases that occur after admission, these cases should be eliminated from the hospital-level PSI by adding exclusion criteria for diagnosis of selected infections in the principal diagnosis field.

Conclusions

These findings, that the hospital-level PSI undercounts cases of infection, help inform policy on two issues. First, it is important for hospitals and physicians to be aware that even though a patient who has undergone a procedure requiring an intravascular device does not acquire an infection during the index admission, this does not mean the patient is not still at risk. This argues for closer monitoring of patients postdischarge and making patients aware of the symptoms of intravascular device-related infections so they can be treated at the earliest possible time. Second, these findings underscore the need to develop data systems that can track patients across multiple admissions for the purpose of identifying complications that result in short-term readmissions. States with administrative databases similar to New York's SPARCS should develop unique patient identifiers that facilitate tracking patients across multiple admissions. Based on our analysis of cases identified with the Selected Infections Due to Medical Care PSI, in the absence of unique identifiers, 75 percent of the patients who are readmitted for care can be identified using only the medical record number and the hospital identification code.

We look forward to future efforts to identify how existing administrative data systems can be used to identify adverse events as completely and as accurately as possible. This task is critical in the all-important quest to optimize the safety and quality of health care in this country.

Acknowledgments

This research was supported by the New York State Department of Health, Health Research Incorporated, and the Agency for Healthcare Research and Quality, under Grant No. U18 HS11880. The views expressed are solely those of the authors.

We thank A. Caton for her initial examination of New York State discharge data.

Author affiliations

All of the authors are affiliated with the Department of Health Policy, Management, and Behavior, University at Albany School of Public Health, Rensselaer, NY.

Address correspondence to: Brian Gallagher, M. S.; Department of Health Policy, Management, and Behavior, University at Albany School of Public Health, One University Place, Rensselaer, NY 12144-3456. Phone: 518-402-4091; fax: 518-402-0414; e-mail: Bxg04@health.state.ny.us.

References