Abstract
Introduction
Risk adjusted thirty-day hospital readmission rate is a commonly used benchmark for hospital quality of care and for Medicare reimbursement. Persons living with HIV (PLWH) may have high readmission rates. This study compared 30-day readmission rates by HIV status in a multi-state sample with planned subgroup comparisons by insurance and diagnostic categories.
Methods
Data for all acute care, non-military hospitalizations in 9 states in 2011 were obtained from the Healthcare Costs and Utilization Project. The primary outcome was readmission for any cause within 30 days of hospital discharge. Factors associated with readmission were evaluated using multivariate logistic regression.
Results
5,484,245 persons, including 33,556 (0.6%) PLWH, had a total of 6,441,695 index hospitalizations, including 45,382 (0.7%) among PLWH. Unadjusted readmission rates for hospitalizations of HIV-uninfected persons and PLWH were 11.2% (95% CI: 11.2, 11.2) and 19.7% (19.3, 20.0), respectively. After adjustment for age, gender, race, insurance, and diagnostic category, HIV was associated with 1.50 (1.46, 1.54) times higher odds of readmission. Predicted, adjusted readmission rates were higher for PLWH within every insurance category, including Medicaid (12.9% [12.8, 13.0] and 19.1% [18.4, 19.7] for HIV-uninfected persons and PLWH, respectively) and Medicare (13.2% [13.1, 13.3] and 18.0% [17.4, 18.7], respectively) and within every diagnostic category.
Discussion
HIV is associated with significantly increased readmission risk independent of demographics, insurance, and diagnostic category. The 19.7% 30-day readmission rate may serve as a preliminary benchmark for assessing quality of care of PLWH. Policymakers may consider adjusting for HIV when calculating a hospital’s expected readmission rate.
Keywords: Hospital readmission, Healthcare utilization, Medicare, Medicaid
INTRODUCTION
Healthcare providers, payers, and policymakers around the world are increasingly using 30-day hospital readmission rate as a quality of care benchmark.(1-6) Among United States (US) adults under 65 years-old, approximately 13% of all-cause hospitalizations are followed by a readmission within 30 days.(7) Among Medicare beneficiaries 65 and over, the readmission rate is approximately 20%.(8) Many 30-day readmissions are thought to be preventable, and preventing readmissions may reduce morbidity and save tens of billions of dollars annually.(8) To motivate hospitals to decrease readmissions, Medicare has implemented public reporting of readmission rates for select diagnoses, including pneumonia, myocardial infarction, and congestive heart failure, and has implemented payment penalties for hospitals that deviate too far above their expected risk-adjusted rate.(9)
In the US, there are over 1.2 million persons living with HIV (PLWH), and the prevalence is increasing steadily.(10) PLWH may be readmitted more frequently than comparable HIV-uninfected persons. A study in 9 HIV clinics found a 19.3% overall 30-day readmission rate, and a single-clinic study, a 25.2% rate.(11,12) Both studies lacked HIV-uninfected comparators, and both were restricted to PLWH actively following-up (engaged) at HIV specialty clinics.
Our objective was to compare readmission rates between HIV-uninfected persons and PLWH using a large, multi-state database. HIV causes unique risk for infectious illness, and it is possible that readmission rates might differ by HIV status, especially for infectious disease hospitalizations. We therefore compared readmission rates by HIV status within broad diagnostic categories. Additionally, while the Centers for Medicare and Medicaid Services (CMS) have so far focused readmission reduction incentives on Medicare enrollees 65-years-and-older, most PLWH are not in this group. Including HIV status might be appropriate when developing risk-adjusted readmission guidelines for other groups with public insurance (for example, Medicaid enrollees). We therefore compared all-cause readmission rates by HIV status within different insurance categories. We also compared readmission rates by HIV status specifically for index hospitalizations for pneumonia (a common diagnosis among PLWH) for Medicaid enrollees and for Medicare enrollees under age 65. We focused on pneumonia hospitalizations because PLWH are hospitalized more frequently for pneumonia than for the other conditions targeted by CMS.(13)
METHODS
We obtained hospital discharge data for 2011 from the State Inpatient Databases (SID), Healthcare Cost and Utilization Project (HCUP).(14) SID data include all discharge diagnoses, patients’ gender, age, race/ethnicity, and primary source of payment for all inpatient stays in all acute-care, non-psychiatric, non-Federal hospitals in participating states. This generally includes all hospitals used by civilians. Federal hospitals are those for active military or veterans (and together constitute <5% of US hospitals).(15)
In 2011, 23 SID states provided “VisitLink,” an encrypted identifier that enables linking of inpatient episodes for the same individual.(16) We selected states that had at least 300,000 discharge records for persons aged 18-64. We excluded NY, which did not provide VisitLink for PLWH, and IN which had a low verification rate for VisitLink. The nine included states were CA, FL, GA, LA, MA, MO, TN, VA, and WA.
Index Hospitalizations
The interval between hospitalizations was the number of days between a discharge and the next admission. Following the methodology used by Medicare,(17) index hospitalizations were defined as having a live discharge and being either the first hospitalization for an individual in 2011 or any subsequent hospitalization preceded by an interval >30 days. Readmissions were hospitalizations with an interval of 1-30 days. If an admission occurred on the same day as a discharge (zero interval), the admission was considered a transfer and combined with the previous hospitalization. Readmissions ending in death were included. Readmissions themselves could not be index hospitalizations. An index hospitalization could be followed by multiple (“linked”) readmissions.
We implemented several exclusion criteria. Observations (n=1,295) missing age data or for persons ≤17 years-old were excluded. Records missing VisitLink (4.4% of records for persons ≥18) were excluded. The definition of index hospitalization necessitated removing admissions that occurred in January, or in 2010, which could be readmissions for a prior event. To have a full 30-day observation period for readmission, index hospitalizations with a December discharge were excluded. Any readmission linked to an out-of-scope index hospitalization was also excluded.
Identification of PLWH
Hospitalizations with any International Classification of Diseases, ninth edition (ICD-9) diagnosis code of 042 (“symptomatic” HIV) or V08 (“asymptomatic”) were identified as occurring to a PLWH. This procedure has been used in prior analyses of HCUP data.(18-20) If a person had one hospitalization with an HIV code, even if the hospitalization met exclusion criteria, this person was considered a PLWH for all other hospitalizations, including any that lacked 042 or V08 codes.
Independent Variables
Following previous methods, the first-listed discharge diagnosis was considered the reason for hospitalization, unless it was HIV infection, thrush (112.0), or chronic Hepatitis C (070.44, 070.54, 070.70, 070.71).(13,21) In these cases, the highest-listed other diagnosis was assigned as the reason for hospitalization.
We classified each reason for hospitalization into 17 diagnostic categories using multi-level Clinical Classification Software (CCS), which groups ICD-9 codes into broader, clinically meaningful categories.(22) We modified the CCS categories in two ways.(13,21) First, infections were reassigned from end-organ system categories to the “infection” category (e.g., cellulitis was reassigned from “dermatologic” to “infection”). Second, we created a separate category for AIDS-defining illnesses (ADI) using the Centers for Disease Control and Prevention list of conditions.(23) This category applied both to HIV-uninfected persons and PLWH. Among HIV-uninfected persons, recurrent pneumonia, encephalopathy not otherwise specified, failure to thrive, and cervical cancer were the most frequent individual diagnoses within the ADI category, and together made up 66% of admissions in this category. While these conditions are ADI’s when occurring to PLWH, they are relatively common among persons with intact immune function, which is consistent with correct ascertainment of HIV-status for these hospitalizations. (In contrast, the four most frequent individual ADI’s among PLWH were Pneumocystosis, Candidal esophagitis, Cryptococcal meningitis, and recurrent pneumonia, together making up 52% of ADI admissions for this group.) After removing infectious ADIs from the infection category, the infection category was renamed “non-AIDS infection”.
In analyses examining readmission rates following pneumonia hospitalizations, we defined pneumonia according to the ICD-9 codes (480-483, 485, 486, 487.0) used by Medicare,(24) and we considered all pneumonia index hospitalizations whether they were classified as ADI or non-AIDS infection.
Age at hospitalization was categorized as 18-34, 35-44, 45-54, 55-64, and ≥65 years-old. Race/ethnicity categories were White, African American, Hispanic, Asian or Pacific Islander, Native American, or other. Records with missing race/ethnicity (114,463) were combined with “other” race/ethnicity. Insurance was coded as Medicare, Medicaid, private, self-pay (including lack of insurance), no charge, or other (for example, workers’ compensation, uniformed services coverage, county indigent programs); 15,467 records missing insurance were combined with “other”.
Analyses
The primary unit of analysis was the index hospitalization. Due to small samples, index hospitalizations in the congenital (10,531 total, 34 among PLWH), perinatal (23, 0), or missing (833, 19) diagnostic categories were removed from analyses. All data for an individual were removed if any index hospitalization had data anomalies, such as a negative interval (n = 4,215). Index episodes ending in death were ineligible (n= 11,397). The final sample of index hospitalizations numbered 6,441,695.
The dichotomous dependent variable was whether an index hospitalization had one or more readmissions. Unadjusted readmission rates were computed for each covariate, stratified by HIV status. Multivariate logistic regression examined the association between readmission and HIV status, adjusting for covariates. A second multivariate model separately interacted HIV status with (1) insurance and (2) diagnostic category. To aid in interpreting the interaction effects, we estimated marginal predicted probabilities for each combination of variables.(25)
All regression models included dichotomous indicators for state, with CA as the reference; including these indicators captures between-state variation in readmission rates. All models adjusted for within-person correlation arising from multiple index hospitalizations by using robust standard errors, clustered on person. Analyses used STATA 12.1 with a 5% significance level (Stata Corp, College Station, Texas).(26)
Sensitivity Analyses
CA expunged V08 codes prior to submission to the SID. Although this resulted in misclassification of some hospitalizations from PLWH to HIV-uninfected, we included CA in our primary analysis because, nationally, it has the second-highest number of PLWH.(27) We performed a sensitivity analysis that removed CA.
Based on previous studies, we expected that obstetric/gynecologic index hospitalizations would be relatively more frequent among HIV-uninfected than among PLWH and would also have a relatively low rate of readmission.(7,11) A second pre-planned sensitivity analysis removed this diagnostic category.
RESULTS
The analytic sample comprised 5,484,245 persons, of whom 33,556 (0.6%) were PLWH. The mean number of index hospitalizations was 1.17 (95% CI: 1.17, 1.17 [end-points identical due to rounding]) for HIV-uninfected persons, and 1.35 (1.34, 1.36) for PLWH. Among HIV-uninfected persons, 86% had only one index hospitalization, 11.2% had 2, 2.3% had 3, and 0.5% had 4-8. Among PLWH, 73.9% had one index hospitalization, 18.7% had 2, 5.9% had 3, and 1.5% had 4-8.
Table 1 shows descriptive characteristics of the 6,441,695 index hospitalizations, 0.7% (45,382) of which were for PLWH. Compared to index hospitalizations for HIV-uninfected persons, hospitalizations for PLWH were more likely to be for males, persons 35-64 years-old, African-Americans, and persons covered by Medicaid. Thirty-three percent of index hospitalizations among PLWH were covered by Medicaid, versus 15% for HIV-uninfected persons. The five most-frequent diagnostic categories for index hospitalizations of HIV-uninfected persons were (in order) cardiovascular, obstetric/gynecologic, non-AIDS infection, gastrointestinal/liver, and injury/poisoning. For PLWH, they were non-AIDS infection, psychiatric, cardiovascular, gastrointestinal/liver, and pulmonary.
Table 1.
Characteristics of index hospitalizations in 9 States in 2011
| Variable | Index Hospitalizations for HIV-uninfected Persons (N = 6,396,313) | Index Hospitalizations for HIV-infected Persons (N = 45,382) |
|---|---|---|
| Gender | ||
| Male | 2,494,314 (39) | 30,086 (66) |
| Female | 3,901,999 (61) | 15,296 (34) |
| Age (years) | ||
| 18 – 34 | 1,353,589 (21) | 7,192 (16) |
| 35 – 44 | 656,248 (10) | 10,653 (24) |
| 45 – 54 | 853,295 (13) | 16,564 (37) |
| 55 – 64 | 1,006,475 (16) | 8,175 (18) |
| ≥ 65 | 2,526,706 (40) | 2,798 (6) |
| Race / Ethnicity | ||
| Non-Hispanic White | 4,254,698 (67) | 15,261 (34) |
| Non-Hispanic Black | 927,246 (15) | 23,603 (52) |
| Hispanic | 747,189 (12) | 5,089 (11) |
| Asian / Pacific Islander | 218,544 (3) | 327 (1) |
| Native American | 18,866 (0.3) | 111 (0.3) |
| Other / Missing | 229,770 (4) | 991 (2) |
| Insurance | ||
| Medicare* | 2,820,349 (44) | 16,064 (35) |
| Medicaid | 974,850 (15) | 15,015 (33) |
| Private | 1,909,545 (30) | 7,072 (16) |
| Self-pay | 334,702 (5) | 4,134 (9) |
| No charge | 96,299 (2) | 961 (2) |
| Other / Missing | 260,568 (4) | 2,136 (5) |
| Number of Readmissions | ||
| 0 | 5,680,374 (89) | 36,460 (80) |
| 1 | 547,371 (9) | 5,998 (13) |
| 2 | 112,145 (2) | 1,648 (4) |
| 3 | 32,711 (1) | 602 (1) |
| 4 | 12,056 (0.2) | 278 (0.6) |
| 5 | 5,241 (0.1) | 155 (0.3) |
| 6 – 35 | 6,415 (0.1) | 214 (0.5) |
| State | ||
| CA | 1,887,380 (30) | 7,872 (17) |
| FL | 1,421,958 (22) | 17,168 (38) |
| GA | 586,960 (9) | 6,662 (15) |
| LA | 304,807 (5) | 2,410 (5) |
| MA | 457,021 (7) | 3,170 (7) |
| MO | 452,248 (7) | 1,724 (4) |
| TN | 458,902 (7) | 2,401 (5) |
| VA | 465,495 (7) | 2,674 (6) |
| WA | 361,542 (6) | 1,301 (3) |
| Diagnostic Category | ||
| AIDS-defining Illness | 23,239 (0.4) | 2,413 (5) |
| Non-AIDS infection | 777,008 (12) | 10,960 (24) |
| Oncologic | 322,921 (5) | 1,475 (3) |
| Endocrine / Metabolic / Nutritional / Immune | 237,220 (4) | 2,204 (5) |
| Hematologic | 76,410 (1) | 1,314 (3) |
| Psychiatric | 420,129 (7) | 5,129 (11) |
| Neurologic | 138,806 (2) | 1,329 (3) |
| Cardiovascular | 1,118,486 (18) | 4,871 (11) |
| Pulmonary | 308,905 (5) | 2,800 (6) |
| Gastrointestinal / Liver | 653,995 (10) | 4,005 (9) |
| Renal / Genitourinary | 250,638 (4) | 2,306 (5) |
| Obstetric / Gynecologic | 957,261 (15) | 1,190 (3) |
| Dermatologic | 15,280 (0.2) | 222 (0.5) |
| Musculoskeletal | 454,571 (7) | 1,436 (3) |
| Injury / Poisoning | 492,832 (8) | 2,469 (5) |
| Symptomatic | 127,429 (2) | 1,068 (2) |
| Unclassified | 21,183 (0.3) | 191 (0.4) |
Entries are numbers of index hospitalizations (column percentage)
Medicare includes Medicare / Medicaid dually enrolled
By Chi-squared test, HIV status is significantly associated (p<0.001) with each variable
Factors Associated with Readmission
Among hospitalizations for HIV-uninfected persons, 11.2% (11.2, 11.2) were followed by readmission within 30 days, compared with 19.7% (19.3, 20.0) of hospitalizations for PLWH (Table 2). Among index hospitalizations with one or more readmissions, the mean number of readmissions was 1.39 (1.39, 1.39) for HIV-uninfected and 1.69 (1.66, 1.73) for PLWH. After adjustment for demographics and reason for hospitalization, the odds of readmission were 1.50 (1.46, 1.54) times higher for index hospitalizations of PLWH than for uninfected persons (Table 3). Demographic factors with strong independent associations included male gender, age >34, Black or Native American race (vs. White race), and Medicare or Medicaid insurance. The adjusted odds of readmission varied by diagnostic category and were higher for ADI than for most other categories.
Table 2.
Unadjusted percentages of index hospitalizations with any readmission by HIV status
| Variable | Index Hospitalizations for HIV-uninfected Persons (N = 6,396,313) | Index Hospitalizations for HIV-infected Persons (N = 45,382) |
|---|---|---|
| Overall | 11.2 (11.2, 11.2) | 19.7 (19.3, 20.0) |
| Gender | ||
| Female | 10.0 (10.0, 10.0) | 19.0 (18.3, 19.7) |
| Male | 13.1 (13.0, 13.1) | 20.0 (19.5, 20.5) |
| Age (years) | ||
| 18 – 34 | 6.1 (6.1, 6.2) | 18.3 (17.4, 19.3) |
| 35 – 44 | 8.9 (8.8, 8.9) | 20.5 (19.7, 21.5) |
| 45 – 54 | 11.5 (11.4, 11.6) | 19.6 (18.9, 20.2) |
| 55 – 64 | 12.2 (12.1, 12.3) | 19.2 (18.3, 20.1) |
| ≥ 65 | 14.0 (14.0, 14.0) | 21.5 (19.9, 23.0) |
| Race / Ethnicity | ||
| Non-Hispanic White | 11.4 (11.4, 11.4) | 18.9 (18.2, 19.5) |
| Non-Hispanic Black | 12.2 (12.2, 12.3) | 19.9 (19.4, 20.5) |
| Hispanic | 10.1 (10.0, 10.2) | 21.5 (20.3, 22.7) |
| Asian / Pacific Islander | 9.5 (9.3, 9.6) | 20.2 (15.9, 24.5) |
| Native American | 11.4 (0.9, 11.9) | 18.0 (11.1, 25.0) |
| Other / Missing | 8.6 (8.5, 8.8) | 16.0 (13.8, 18.3) |
| Insurance | ||
| Medicare* | 14.7 (14.6, 14.7) | 21.4 (20.7, 22.1) |
| Medicaid | 10.5 (10.4, 10.6) | 21.5 (20.8, 22.2) |
| Private | 7.3 (7.3, 7.3) | 15.4 (14.6, 16.3) |
| Self-pay | 8.6 (8.5, 8.7) | 15.1 (14.0, 16.2) |
| No charge | 10.2 (10.0, 10.4) | 19.9 (17.3, 22.5) |
| Other / Missing | 8.7 (8.6, 8.8) | 16.8 (14.9, 18.1) |
| State | ||
| CA | 11.0 (10.9, 11.0) | 23.3 (22.3, 24.2) |
| FL | 12.0 (11.9, 12.1) | 20.6 (20.0, 21.3) |
| GA | 10.2 (10.1, 10.3) | 18.0 (17.0, 18.9) |
| LA | 11.4 (11.3, 11.5) | 16.3 (14.8, 17.9) |
| MA | 12.1 (12.0, 12.2) | 18.6 (17.2, 20.1) |
| MO | 11.4 (11.3, 11.5) | 16.2 (14.4, 18.1) |
| TN | 11.2 (11.1, 11.3) | 16.1 (14.6, 17.6) |
| VA | 10.9 (10.8, 11.0) | 18.8 (17.3, 20.4) |
| WA | 9.6 (9.5, 9.7) | 15.3 (13.3, 17.3) |
| Diagnostic Category | ||
| AIDS-defining Illness | 18.2 (17.7, 18.7) | 20.5 (18.9, 22.1) |
| Non-AIDS infection | 13.6 (13.5, 13.7) | 17.0 (16.3, 17.7) |
| Oncologic | 15.1 (15.0, 15.2) | 32.4 (30.0, 34.8) |
| Endocrine / Metabolic / Nutritional / Immune | 13.9 (13.8, 14.0) | 23.0 (21.3, 24.8) |
| Hematologic | 17.7 (17.4, 18.0) | 21.8 (19.5, 24.0) |
| Psychiatric | 13.7 (13.6, 13.8) | 24.3 (23.0, 25.5) |
| Neurologic | 10.9 (10.7, 11.0) | 18.8 (16.7, 20.9) |
| Cardiovascular | 13.0 (12.9, 13.0) | 18.6 (17.5, 19.8) |
| Pulmonary | 15.9 (15.8, 16.0) | 21.0 (19.4, 22.5) |
| Gastrointestinal / Liver | 11.9 (11.8, 11.9) | 19.8 (18.5, 21.0) |
| Renal / Genitourinary | 12.0 (11.8, 12.1) | 22.0 (20.3, 23.7) |
| Obstetric / Gynecologic | 3.6 (3.5, 3.6) | 9.0 (7.3, 10.7) |
| Dermatologic | 15.6 (15.0, 16.2) | 25.2 (19.5, 30.9) |
| Musculoskeletal | 6.3 (6.3, 6.4) | 12.8 (11.1, 14.5) |
| Injury / Poisoning | 11.0 (10.8, 11.1) | 16.8 (15.4, 18.3) |
| Symptomatic | 11.6 (11.4, 11.7) | 18.7 (16.4, 21.1) |
| Unclassified | 12.3 (11.9, 12.7) | 20.4 (15.4, 26.2) |
Entries are percentage (95% confidence interval) of index hospitalizations with one or more readmissions. Denominators for percentages appear in Table 1.
Medicare includes Medicare / Medicaid dually enrolled
Table 3.
Multivariate logistic regression of thirty-day readmissions
| Variable | Adjusted Odds Ratio (95% CI) |
|---|---|
| HIV Status | |
| Uninfected (referent) | 1.00 |
| Infected | 1.50 (1.46, 1.54) |
| Gender | |
| Female | 0.89 (0.88, 0.90) |
| Male (referent) | 1.00 |
| Age (years) | |
| 18 – 34 (referent) | 1.00 |
| 35 – 44 | 1.12 (1.10, 1.13) |
| 45 – 54 | 1.22 (1.21, 1.24) |
| 55 – 64 | 1.31 (1.29, 1.32) |
| ≥ 65 | 1.19 (1.18, 1.21) |
| Race / Ethnicity | |
| Non-Hispanic White (referent) | 1.00 |
| Non-Hispanic Black | 1.13 (1.12, 1.14) |
| Hispanic | 0.97 (0.96, 0.98) |
| Asian / Pacific Islander | 0.94 (0.93, 0.95) |
| Native American | 1.09 (1.04, 1.15) |
| Other / Missing | 0.86 (0.85, 0.87) |
| Insurance | |
| Medicare* (referent) | 1.00 |
| Medicaid | 0.98 (0.97, 0.99) |
| Private | 0.57 (0.57, 0.58) |
| Self-pay | 0.56 (0.55, 0.57) |
| No charge | 0.64 (0.62, 0.65) |
| Other / Missing | 0.63 (0.62, 0.64) |
| State | |
| CA (referent) | 1.00 |
| FL | 1.01 (1.00, 1.02) |
| GA | 0.78 (0.76, 0.80) |
| LA | 0.99 (0.98, 1.00)† |
| MA | 1.03 (1.02, 1.04) |
| MO | 0.98 (0.97, 0.99) |
| TN | 0.94 (0.93, 0.95) |
| VA | 0.97 (0.96, 0.98) |
| WA | 0.93 (0.92, 0.94) |
| Diagnostic Category | |
| AIDS-defining Illness (referent) | 1.00 |
| Non-AIDS infection | 0.75 (0.72, 0.77) |
| Oncologic | 0.92 (0.89, 0.95) |
| Endocrine / Metabolic / Nutritional / Immune | 0.80 (0.77, 0.83) |
| Hematologic | 1.03 (0.99, 1.07)† |
| Psychiatric | 0.85 (0.82, 0.88) |
| Neurologic | 0.60 (0.58, 0.62) |
| Cardiovascular | 0.68 (0.66, 0.71) |
| Pulmonary | 0.86 (0.83, 0.89) |
| Gastrointestinal / Liver | 0.69 (0.67, 0.72) |
| Renal / Genitourinary | 0.69 (0.66, 0.71) |
| Obstetric / Gynecologic | 0.25 (0.24, 0.26) |
| Dermatologic | 0.86 (0.81, 0.90) |
| Musculoskeletal | 0.34 (0.33, 0.35) |
| Injury / Poisoning | 0.62 (0.60, 0.64) |
| Symptomatic | 0.63 (0.61, 0.65) |
| Unclassified | 0.69 (0.65, 0.72) |
Medicare includes Medicare / Medicaid dually enrolled
All adjusted odds ratios are statistically significant, p < 0.05, except those marked by an †
A final multivariate model added two interaction terms to the model presented in Table 3: HIV status by insurance and HIV status by diagnostic category (the Supplemental Digital Table reports complete model results). Table 4 shows this model’s marginal predicted probabilities, in other words, estimated absolute readmission rates adjusted for all other covariates. The predicted risk differences (with confidence intervals) allow direct comparisons between PLWH and HIV-uninfected persons within individual insurance and diagnostic categories.
Table 4.
Marginal predicted readmission rates from multivatiate logistic regression
| HIV Status | Predicted Risk Difference | ||
|---|---|---|---|
| Uninfected | Infected | ||
| Insurance | |||
| Medicare | 13.2 (13.1, 13.3) | 18.0 (17.4, 18.7) | 4.8 (4.2, 5.8) |
| Medicaid | 12.9 (12.8, 13.0) | 19.1 (18.4, 19.7) | 6.2 (5.4, 6.8) |
| Private | 8.1 (8.0, 8.1) | 13.4 (12.6, 14.1) | 5.3 (4.5, 6.1) |
| Self-pay | 7.9 (7.8, 8.0) | 13.7 (12.7, 14.8) | 5.8 (4.8, 6.9) |
| No charge | 8.8 (8.7, 9.0) | 17.1 (14.7, 19.3) | 8.2 (5.9, 10.5) |
| Other / Missing | 8.7 (8.6, 8.8) | 14.2 (12.7, 15.6) | 5.4 (4.0, 6.8) |
| Diagnostic Category | |||
| AIDS-defining Illness | 16.6 (16.2, 17.1) | 19.0 (17.4, 20.5) | 2.3 (0.7, 3.9) |
| Non-AIDS infection | 12.8 (12.7, 12.9) | 15.4 (14.7, 16.0) | 2.6 (1.9, 3.3) |
| Oncologic | 15.2 (15.0, 15.3) | 29.3 (27.0, 31.6) | 14.1 (11.8, 16.4) |
| Endocrine / Metabolic / Nutritional / Immune | 13.5 (13.4, 13.7) | 20.3 (18.7, 22.0) | 6.8 (5.2, 8.5) |
| Hematologic | 16.7 (16.4, 17.0) | 19.9 (17.8, 22.1) | 3.2 (1.0, 5.4) |
| Psychiatric | 14.2 (14.1, 14.4) | 21.7 (20.5, 22.9) | 7.4 (6.3, 8.6) |
| Neurologic | 10.5 (10.4, 10.7) | 16.7 (14.8, 18.7) | 6.2 (4.3, 8.1) |
| Cardiovascular | 11.8 (11.8, 11.9) | 16.2 (15.1, 17.2) | 4.3 (3.3, 5.3) |
| Pulmonary | 14.4 (14.3, 14.5) | 18.2 (16.8, 19.5) | 3.8 (2.4, 5.2) |
| Gastrointestinal / Liver | 11.9 (11.9, 12.0) | 17.9 (16.8, 19.0) | 5.9 (4.8, 7.1) |
| Renal / Genitourinary | 11.8 (11.7, 11.9) | 19.4 (17.8, 20.9) | 7.5 (6.0, 9.1) |
| Obstetric / Gynecologic | 4.7 (4.6, 4.8) | 9.0 (7.3, 10.8) | 4.3 (2.6, 6.1) |
| Dermatologic | 14.3 (13.7, 14.8) | 22.4 (17.1, 27.6) | 8.1 (2.8, 13.3) |
| Musculoskeletal | 6.2 (6.1, 6.3) | 11.4 (10.0, 13.0) | 5.2 (3.7, 6.8) |
| Injury / Poisoning | 10.8 (10.7, 10.9) | 15.1 (13.7, 16.4) | 4.2 (2.9, 5.6) |
| Symptomatic | 11.0 (10.8, 11.1) | 16.6 (14.5, 18.8) | 5.6 (3.5, 7.8) |
| Unclassified | 11.8 (11.4, 12.2) | 17.8 (12.6, 23.0) | 6.0 (0.8, 11.2) |
Entries are percentages (95% CI) from a multivariate model including all variables in Table 3 and with HIV status interacted with insurance and with diagnostic category (see Supplemental Digital Table for full logistic results).
Within each category of insurance, predicted readmission rates were consistently higher for PLWH than for HIV-uninfected persons. The mean predicted absolute risk of readmission for hospitalizations of HIV-uninfected persons with Medicare was 13.2% (13.1%, 13.3%) and was 18.0% (17.4%, 18.7%) for PLWH with Medicare. Hence PLWH had 4.8 percentage points (4.2, 5.8) higher absolute risk of readmission than HIV-uninfected. Hospitalizations of PLWH with Medicaid were predicted to have 6.2 (5.4, 6.8) percentage points higher absolute risk of readmission than HIV-uninfected with Medicaid.
Within each diagnostic category, hospitalizations for PLWH had higher predicted mean readmission risk than those for HIV-uninfected persons (Table 4). The five categories with the largest differences in absolute risk of readmission were oncologic (14.1 [11.8, 16.4]) percentage points, dermatologic (8.1 [2.8, 13.3]), renal/genitourinary (7.5 [6.0, 9.1]), psychiatric (7.4 [6.3, 8.6]), and endocrine/metabolic/nutritional/immune (6.8 [5.2, 8.5]).
We investigated whether the large risk difference for the oncologic category may have been primarily due to hospitalizations for lymphoma, which is strongly associated with HIV.(28) Among all lymphoma-related hospitalizations (CCS Levels 2.10.1 and 2.10.2), the observed readmission rate was 29.5% for HIV-uninfected and 40.9% for PLWH. However, respective readmission rates were 14.8% and 31.1% for other oncologic hospitalizations, indicating that higher oncologic readmission rates for PLWH were not limited to lymphoma.
Among 15,676 pneumonia index hospitalizations occurring to Medicaid enrollees, 1,094 (7.0%) occurred among PLWH. The unadjusted risk of readmission was 14.3% for HIV-uninfected and 16.2% for PLWH, yielding an OR for HIV-infection of 1.15 (0.98, 1.37). Among 16,305 pneumonia index hospitalizations occurring to Medicare enrollees younger than 65 years-old, 726 (4.4%) occurred among PLWH. The unadjusted readmission risks were 16.1% for HIV-uninfected and 16.9% for PLWH, OR 1.06 (0.87, 1.30).
First Readmission Diagnoses
The diagnostic category for the first readmission was examined for the 724,861 index hospitalizations followed by any readmission. (If a chain of 2 or more readmissions occurred, only the first was considered.) A total of 306,784 of 715,939 (43%) first readmissions were in the same diagnostic category as the associated index hospitalization for HIV-uninfected and 3,556 of 8,922 (40%) for PLWH. The frequency that readmissions were in the same category as index hospitalizations varied across diagnostic categories (Table 5). The diagnostic categories for which first readmissions were most likely to match the index hospitalization category were obstetric/gynecologic (94% and 85% for HIV-uninfected and PLWH, respectively) and psychiatric (74%, 72%). For instances with <50% matching, there were no cases where a majority of first readmissions occurred in another single category. For example, for ADI among PLWH (33% matching), 22% of first readmissions were for non-AIDS infections, 7% for pulmonary and 6% or less for all other categories (results not shown).
Table 5.
Percentages of first readmissions occurring in the same diagnostic category as the associated index hospitalization
| HIV-uninfected | HIV-infected | |||
|---|---|---|---|---|
| Denominator N | % | Denominator N | % | |
| Overall | 715,939 | 43 | 8,922 | 40 |
| Diagnostic Category | ||||
| AIDS-defining Illness | 4,234 | 17 | 495 | 33 |
| Non-AIDS infection | 105,583 | 40 | 1,864 | 39 |
| Oncologic | 48,837 | 38 | 478 | 44 |
| Endocrine / Metabolic / Nutritional / Immune | 32,966 | 30 | 508 | 28 |
| Hematologic | 13,514 | 31 | 286 | 26 |
| Psychiatric | 57,448 | 74 | 1,244 | 72 |
| Neurologic | 15,075 | 25 | 250 | 27 |
| Cardiovascular | 144,878 | 50 | 908 | 42 |
| Pulmonary | 49,118 | 43 | 587 | 36 |
| Gastrointestinal / Liver | 77,606 | 41 | 792 | 39 |
| Renal / Genitourinary | 30,010 | 22 | 508 | 29 |
| Obstetric / Gynecologic | 34,145 | 94 | 107 | 85 |
| Dermatologic | 2,381 | 19 | 56 | 14 |
| Musculoskeletal | 28,745 | 17 | 184 | 10 |
| Injury / Poisoning | 54,070 | 27 | 416 | 25 |
| Symptomatic | 14,723 | 13 | 200 | 12 |
| Unclassified | 2,606 | 6 | 39 | 3 |
Sensitivity Analyses
In a sensitivity analysis excluding CA, the percentages of index hospitalizations with readmissions were 11.3% and 18.9% for HIV-uninfected and PLWH, respectively. The AOR for HIV-infected status in a model similar to that in Table 3 was 1.47 (1.43, 1.51).
As expected, obstetric/gynecologic index hospitalizations were relatively more frequent among HIV-uninfected (15% of all index hospitalizations vs. 2.6% among PLWH) and also had relatively low unadjusted readmission rates (3.6% and 9.0%, respectively). In a sensitivity analysis removing this diagnostic category (n=967,833), the overall readmission rates for the remaining index hospitalizations were 12.5% (12.5, 12.6) for HIV-uninfected and 19.9% (19.6, 20.3) for HIV- infected. The AOR in a model similar to that in Table 3 was 1.49 (1.46, 1.53).
Some prior analyses have included readmission hospitalizations themselves as index hospitalizations. Using this methodology, we obtained a comparable rate of 13.5% (13.4, 13.6) for HIV-uninfected persons and 25.2% (24.6, 25.7) for HIV- infected persons. The readmission rate for readmissions was higher than that for (initial) index hospitalizations (29.1% for HIV-uninfected and 42.2% for HIV- infected, n=956,279 and 14,671, respectively).
Additionally, negative binomial regression analyses (not shown) of the total number of readmissions occurring in a chain following an index hospitalization (with each readmission interval <=30 days) produced a pattern of results similar to those from logistic regression.
DISCUSSION
In 9 states in 2011, PLWH had a 76% higher unadjusted readmission rate than HIV-uninfected persons (19.7% vs. 11.2%). The overall readmission rate remained higher for PLWH after adjustment for demographics, insurance, and diagnostic category (adjusted OR 1.50 [1.46, 1.54]). Adjusted rates were higher for PLWH within every insurance type and within every diagnostic category. In over half of all instances, for both HIV-uninfected persons and PLWH, the reason for readmission differed from the reason for index hospitalization.
The 19.7% readmission rate for PLWH resembles the 19.3% rate reported from a consortium of 9 HIV clinics and is lower than the 25.2% rate reported from a single HIV clinic.(11,12) Being in a frail state of health, when new diseases, both infectious and non-infectious, frequently occur (13,29-34) may contribute to the higher rate of readmission among PLWH than among HIV-uninfected persons. We further speculate that lower socioeconomic status(35) and lower health literacy could also contribute to the disparity.
The 19.7% all-cause rate and the unadjusted rates across diagnostic categories, including the 20.5% rate for ADI (Table 2), may be useful as initial quality of care benchmarks. Readmission rates substantially above these values may reflect deficits in inpatient care or in the transition from inpatient to outpatient settings. HIV providers and hospitals may consider interventions such as enhanced patient education, patient navigators, telephone follow-up, nurse home visits, and outpatient follow-up visits in order to bring readmission rates in line with benchmarks.(36-38)
We are uncertain why the difference in risk of readmission by HIV status varied across diagnostic categories. For oncologic hospitalizations, some possible contributors to the large difference in risk by HIV status may include worse overall outcomes among PLWH(39,40), drug interactions and toxicities (41,42), and greater infection risk from the combined immunosuppressive effects of HIV and cytotoxic chemotherapy. Because psychiatric and renal/genitourinary hospitalizations are frequent among PLWH, future studies should evaluate the reasons for large risk differences in these diagnostic categories.
Many persons under 65 years-old enrolled in Medicaid or in Medicare have chronic disabilities. Among PLWH in these programs, the disabling condition is usually AIDS-related.(43,44) In the general population, persons with chronic disabilities that qualify them for Medicaid or Medicare have higher readmission rates than age-matched peers.(7) We had hypothesized this might dilute any difference associated with HIV status specifically for Medicaid and Medicare hospitalizations. However, the differences remained robust in our adjusted analyses.
Because of these robust differences, specific adjustment for HIV may be worth evaluating if future readmission standards are developed for Medicaid and for under-65-Medicare populations. In the case of pneumonia, however, our 9-state sample did not show a significant association between HIV and readmission risk. Nevertheless further evaluation may be warranted. The prevalence of HIV as a comorbidity among Medicaid (7.0%) and among under-65-Medicare (4.4%) index hospitalizations for pneumonia is comparable to that of many comorbidities CMS includes in its risk-adjustment model for pneumonia for 65-and-over-Medicare hospitalizations.(17,24) CMS has been considering incentives to reduce all-cause readmissions among under-65 Medicare beneficiaries undergoing hemodialysis for end-stage renal disease. CMS’ proposed risk-adjustment model would include HIV.(45) In the United Kingdom, general readmission payment penalties exist and are under review.(6,46,47) Knowledge of an expected high rate of readmission among PLWH may be informative to this review.
As in prior studies, we found that, similar to the general population, less than half of readmissions for PLWH occur within the same diagnostic category as the index hospitalization.(8,11) This was not true for every diagnostic category, however, and readmission rates for the same category were relatively high for obstetric and psychiatric index hospitalizations. It is interesting that less than half of readmissions following ADI and non-AIDS infection hospitalizations were within the same respective categories. This argues against the supposition that because of immune suppression, PLWH would be primarily readmitted with relapsing or successive infections and emphasizes that a wide range of comorbid conditions occurs among PLWH.
The present study has several unique strengths. It is the only study with an HIV-uninfected comparator group, thus allowing assessment of HIV independent of substantial variation by state, insurance, age, race, and gender. The sample of HIV hospitalizations in the present study is several times higher than in the previous studies and incorporates rural areas, PLWH who receive HIV care outside of large HIV-specialty clinics, and PLWH who are not engaged in regular HIV care. The latter group is especially important given that half of PLWH in the US are not engaged in care.(48)
Important limitations of our study derive from using ICD-9 codes to assign reason for hospitalization and to ascertain HIV status. The set of codes may have been incomplete or may not have been listed in descending order of importance to causing admission. However, because hospitals are likely to generate lists in the same manner (or to use the same list) for reporting to the SID as for Medicare reporting, we suspect the accuracy of our ascertainment of reasons for hospitalizations resembles the accuracy of Medicare analyses. Also, we suspect that any misclassification of PLWH as HIV-uninfected (in other words, 042 or V08 being omitted from the list of codes) would be much more common than misclassification of HIV-uninfected persons as PLWH by erroneous ICD-9 code assignment. The overall effect of misclassification would, therefore, be to diminish apparent differences in readmission rates between the two groups. Use of ICD-9 codes may also bias the ascertained cause for readmission to being similar to the cause of the index admission. This is because providers may copy forward previous electronic documents to save time. Another limitation is that our sample includes only 9 states. While CA and FL have the 2nd and 3rd most PLWH among all states,(27) our sample cannot be assumed to be nationally or internationally representative. However, while overall readmission rates vary between US states(8) and between countries,(4,5) we have no reason to believe our finding of a significant difference in relative rates between PLWH and HIV-uninfected persons would differ in other settings. Finally, the discharge data do not include variables such as CD4 count or receipt of antiretroviral therapy, which could be associated with the probability of readmission.
In conclusion, our study provides strong evidence that HIV is associated with increased 30-day readmission risk independent of demographic factors, insurance, and reason for index hospitalization. The 19.7% readmission rate from our 9-state sample may be useful as a benchmark for assessing quality of inpatient care of PLWH. Healthcare policymakers and insurers may consider adjusting for HIV when setting future 30-day readmission standards.
Supplementary Material
Acknowledgments
We appreciate the support of the Healthcare Cost and Utilization Project team at the Agency for Healthcare Research and Quality for their help with data and their thoughtful comments on the project.
Source of Funding:
This work was supported by NIH grants K23 AI084854 (SAB) and P30 AI094189 (RDM), and by the Agency for Healthcare Research and Quality [HHSA290201100007C]. The views expressed in this paper are those of the authors. No official endorsement by the Agency for Healthcare Research and Quality is intended or should be inferred.
Footnotes
Conference Presentation: The findings herein were presented, in part, at the 20th Conference on Retroviruses and Opportunistic Infections, March 2013, Atlanta, USA
Conflicts of Interest
S.A.B. has been a consultant for Bristol-Myers Squibb. K.A.G. has been a consultant for Bristol-Myers Squibb and Tibotec, has received research support from Tibotec, and has been an expert witness for the US government. There were no potential conflicts for the remaining authors.
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