Patients admitted to the general medicine and trauma services of two urban hospitals during the fall–winter had 3 times greater odds of having undiagnosed HIV infection than those admitted during the summer. The proportion of patients with undiagnosed HIV was 3.7% in the fall–winter versus only 1.4% in the summer. Seasonal variation in admissions and mortality has also been observed for patients who are hospitalized with other diseases including myocardial infarction, congestive heart failure, asthma, and peptic ulcer disease.9,10,14–19
In regard to HIV-related diseases, Pneumocystis carinii
pneumonia (PCP) has been reported to be more likely during winter months.6
Even in the post-HAART (highly active antiretroviral therapy) era, PCP is still among the most common AIDS-defining conditions at first diagnosis of HIV.20
Yet PCP is unlikely to account for the excess of undiagnosed HIV infection in the fall–winter months in this study because clinicians readily associate this condition with AIDS and would have performed inpatient HIV testing.
Our analysis of the clinical conditions of persons with undiagnosed HIV was limited by the need to ensure the anonymity of our study subjects. Although DRGs and MDCs were developed for billing purposes, we used these data for analysis of clinical conditions because they offered sufficiently large categories that individuals could not be identified. In addition, several studies have evaluated the validity of diagnostic and procedural codes and found that they are a reasonably accurate source of data for clinical analyses.21–23
Although pulmonary infections are more common in winter,24
a composite “infectious diagnoses” MDC including pneumonia among other infectious diagnoses was not associated with undiagnosed HIV infection in the fall–winter cohort. However, undiagnosed HIV infection was significantly more likely in the subset of persons with an “infection” DRG including septicemia, parasitic infections, postoperative infections, and fever of unknown origin. Certainly, HIV-infected persons are predisposed to these infectious conditions.25
However, HIV-infected patients are subject to a wide variety of other infectious and noninfectious complications that may not trigger clinicians to consider the diagnosis of HIV infection.26,27
In our fall–winter cohort, persons with undiagnosed HIV were more likely to be discharged with a renal/genitourinary MDC that includes conditions such as renal failure and genitourinary infections. These are relatively common complications of HIV28–32
but are also highly prevalent in uninfected persons. Persons with undiagnosed HIV were also more likely to be discharged with a dermatologic/breast MDC which includes cellulitis and skin ulcerations that are also more frequently encountered in patients with HIV.33,34
We speculate that the higher prevalence of these conditions among persons with HIV accounts for the differences in HIV prevalence among these MDCs. Because more than two thirds of the patients with undiagnosed HIV infection in our fall–winter cohort were discharged with MDCs other than infection, renal/genitourinary, or dermatologic/breast conditions, targeting persons with only these conditions for HIV testing and counseling would likely have poor sensitivity.
The seroprevalence of undiagnosed HIV infection for trauma patients was lower than that for general medicine patients but this difference did not achieve statistical significance. The seroprevalence in our trauma cohort is on the low end of the range (from 2% to 17%) seen in anonymous seroprevalence studies in emergency departments, with the highest rates for patients with behavioral risks such as male homosexual activity and intravenous drug use.35
In New York City, the seroprevalence of HIV in trauma patients was 7.2% but that study did not exclude known HIV-infected persons and was significantly higher for persons testing positive for cocaine use.36
A limitation of our study is the lack of data on HIV risk behaviors such as injection drug use or male-to-male sex.
Women tended to be less likely to have undiagnosed HIV infection than men, and black persons tended toward being more likely to have HIV undiagnosed infection, although neither association reached statistical significance in the unadjusted or adjusted analysis. Interestingly, black patients constituted a significantly higher proportion of admissions to the study services during the summer months when HIV seroprevalence was lower. Research conducted by the CDC in the early 1990s suggested that routine HIV testing should be conducted in acute care hospitals with an HIV prevalence of at least 1%.37
Our finding of a greater than 1% HIV seroprevalence rate suggests that testing throughout the year is warranted in our setting. However, in many settings where resources are scarce, rather than trying to target specific types of patients for HIV testing, directing testing to the season when undiagnosed HIV is more prevalent among admissions may produce a greater number of newly identified HIV infections. Although screening of inpatients only during the fall–winter months may reduce costs, this strategy poses different logistical and administrative challenges (e.g., hiring and training staff) and may be difficult to orchestrate. Asking about HIV risk behaviors can further increase the yield of testing. However, presenting HIV counseling and testing as routine activity instead of selectively targeting by risk assessment has been associated with higher acceptance rates in a number of diverse settings.38–40
Our conclusions are subject to several additional caveats. Some patients who were classified as having undiagnosed HIV infection could have known their HIV status but not disclosed it to their physician during the hospitalization. Alternatively, the patient might have divulged to the physicians that she or he had HIV but, because it was not considered germane to the reason for admission, HIV was not recorded among any of the maximum of 10 discharge diagnoses. In support of the validity of our results, the seroprevalence of undiagnosed HIV in this study is similar to that observed in another urban hospital in our region.5
Our results are also consistent with findings of previous unlinked serosurveys performed in the past decade.37,41–44,45
In addition, we obtained serum for only slightly more than half of the admissions during the 2 study periods. Sera were less likely to have been tested for admitted patients who were younger or on the trauma service. We can only speculate as to how these differences affect our finding of seasonal differences in the prevalence of undiagnosed HIV infection. Because age was not associated with undiagnosed HIV infection, it is unlikely that this difference at only one hospital could explain the observed seasonal differences. We observed a seasonal difference in HIV seroprevalence in the medicine services of both hospitals, so selection effects due to one service are also unlikely to be responsible for our findings. Regardless, our conclusions regarding these groups should be viewed with circumspection as the seasonal difference could still only reflect random variation.
The results of this study are most likely to be generalizable to larger tertiary care hospitals in areas with higher HIV seroprevalence. In the United States, these regions are the South, Far West, and Northeast.13
These data should increase awareness that HIV among hospitalized patients can remain undiagnosed. A hospital-based counseling and testing program has been shown to increase identification of undiagnosed HIV infection.5,46
The medical benefit of making a new HIV diagnosis is clear for the individual but there is also potential for significant public health benefit.
As stated previously, the CDC has suggested that routine testing should be conducted in acute care hospitals with an HIV prevalence of at least 1%.37
More recent CDC recommendations state that the threshold for routine testing could vary across settings and should consider available resources.47
If other anonymous unlinked seroprevalence studies confirm seasonal variation in undiagnosed HIV infection in inpatients, routine HIV testing of admissions to similar hospitals in regions of higher HIV seroprevalence may be particularly important to conduct during the fall–winter months.