Using the Revised Centers for Disease Control and Prevention Staging System to Classify Persons Living With Human Immunodeficiency Virus in New York City, 2011–2015

Abstract

The proportion of persons living with human immunodeficiency virus (HIV) in New York City in stage 1 (CD4 ≥ 500 cells/mm³) increased from 50.6% in 2011 to 59.6% in 2015. The revised Centers for Disease Control and Prevention staging system of HIV infection is a useful tool with which to classify persons living with HIV.

In Brief

The revised Centers for Disease Control and Prevention staging system of human immunodeficiency virus infection is a useful tool with which to classify persons living with human immunodeficiency virus.

In 2014, the Centers for Disease Control and Prevention (CDC) revised its surveillance case definition for human immunodeficiency virus (HIV) infection.¹ A confirmed case, whether newly diagnosed or established, can be classified into one of four disease stages, 0, 1, 2, or 3. Early infection, defined as a documented negative HIV test within 6 months before diagnosis, is classified as stage 0, regardless of CD4 count; CD4 count of 500 cells/mm³ or greater is classified as stage 1; CD4 count between 200 and 499 cells/mm³ is classified as stage 2; and CD4 count less than 200 cells/mm³ or a stage 3–defining opportunistic illness (e.g., Kaposi sarcoma, pneumocystis pneumonia, and tuberculosis) regardless of CD4 count, is classified as stage 3. Unlike the previous staging system which stipulated that “once AIDS, always AIDS,” regardless of any future improvement in CD4 count or resolution of opportunistic illness, the new staging system allows HIV-infected persons to move back and forth between stages.^1,2

The CDC and local jurisdictions have routinely used the revised staging system to classify persons newly diagnosed with HIV in the United States,³ but few have used the revised staging system to classify persons living with HIV (PLWH).⁴ The purpose of this analysis is to classify PLWH in New York City (NYC) using the revised CDC staging system.

METHODS

Data Source and Analysis Population

The NYC HIV surveillance data were used for the analysis. For each calendar year, the analysis population included PLWH who, (1) were ≥13 years of age by the end of the year, (2) were not known to have died by the end of the year, and (3) had at least 1 CD4/viral load test in NYC in the year. Out-of-care patients were estimated using a previously described statistical weighting method.^5,6 Briefly, the NYC HIV laboratory data reporting system was treated as a special annual population-based survey, lasting from January 1 to December 31 every year. Patients who had at least 1 CD4/viral load test in the year were considered participants in the survey.⁷ Each participant was then given a weight equal to the inverse of the probability that a patient had a CD4/viral load test in NYC in the year. The probability was calculated based on the time interval between the last care visit before the year, or date of diagnosis if no care visits before the year, and the first care visit in the year. If a patient’s interval was 1 year or less, meaning that the patient was in regular care and definitely included in the annual survey in the year with a probability of 100%, the patient received a weight of 1. If a patient’s interval was more than 1 year, the patient received a weight equal to the time interval in years. For example, if a patient had his last care visit exactly 3 years before his first care visit in the year, he received a weight of 3, and the patient not only represented himself, but 2 out-of-care patients.

Measures

Stage of HIV infection of the case was classified based on the last CD4 count value in the year. CD4 count of 500 cells/mm³ or greater was classified as stage 1, CD4 count between 200 and 499 cells/mm³ was classified as stage 2, and CD4 less than 200 cells/mm³ was classified as stage 3.⁸ Patients who were diagnosed with acute HIV infection (stage 0) in the year were classified as stage 1 regardless of their CD4 count values, because (1) the number of such patients was small (157 in 2011, 221 in 2012, 247 in 2013, 228 in 2014, and 208 in 2015), (2) they accounted for a small proportion (<0.5%) of PLWH, and (3) the majority of these patients would be in stage 1 by the end of the year. A small proportion of the analysis population missing CD4 values in the year was excluded from the analysis (1.87% in 2011, 1.73% in 2012, 1.83% in 2013, 1.89% in 2014, and 2.74% in 2015).

Statistical Analysis

All 5-year data were included to describe the trend in the distribution of stage of HIV infection among PLWH in NYC, 2011–2015. The 2015 year data were used to describe the stage of HIV infection among PLWH by demographic and clinical characteristics, and to estimate unadjusted odds ratios (ORs), adjusted ORs (_adjORs) and 95% confidence intervals (CIs) for PLWH being in a lower/healthier stage, using weighted ordinal logistic regression models.

RESULTS

The proportion of PLWH in NYC in stage 1, the healthiest stage, increased from 50.6% (95% CI, 50.3–51.0%) in 2011 to 59.6% (95% CI, 59.3–60.0%) in 2015, and the proportion in stage 3 decreased from 13.4% (95% CI, 13.2–13.7%) in 2011 to 9.9% (95% CI, 9.7–10.1%) in 2015 (Fig. 1).

Figure 1: CDC stages of HIV infection among PLWH in New York City, 2011–2015.

In 2015, by race/ethnicity, white PLWH had the highest proportion (69.7%) and blacks had the lowest proportion (56.9%) in stage 1; by transmission risk, men who have sex with men (MSM) had the highest (64.2%) and persons with perinatal transmission risk (47.2%) had the lowest proportion in stage 1; by year of diagnosis, persons diagnosed before 1991 had the lowest proportion (53.2%) (Table 1).

TABLE 1: CDC Stages of HIV Infection Among PLWH in New York City in 2015, by Characteristics

The multivariable ordinal logistic regression model showed that the odds of being in a lower/healthier stage were higher among females (_adjOR, 1.53; 95% CI, 1.47–1.59) than males and higher among Hispanics (_adjOR, 1.10; 95% CI, 1.06–1.14) and whites (_adjOR, 1.77; 95% CI, 1.69–1.85) than blacks. Persons living with HIV aged 13–17 years had the highest odds (_adjOR, 2.30; 95% CI, 1.67–3.15) and PLWH aged 35 to 44 years had the lowest odds (_adjOR, 0.69; 95% CI, 0.62–0.76) of being in a healthier stage. By transmission risk, MSM were the most likely and persons with perinatal transmission risk were the least likely to be in a healthier stage (_adjOR, 0.33; 95% CI, 0.29–0.38).

DISCUSSION

Using the revised CDC staging system, we described the current clinical status of PLWH and recent trends in NYC. The proportion of PLWH in NYC in stage 1 increased from 50.6% in 2011 to 59.6% in 2015, and the proportion in stage 3 decreased from 13.4% to 9.9%. The improving clinical status among PLWH in NYC may be attributed to ongoing improvements in linkage to care, retention in care and HIV treatment in NYC.^9–14

Despite the overall improvement, there were significant differences across subgroups. Racial disparities are observed in many HIV indicators, and stage of infection is no exception. Compared with whites, blacks and Hispanics were less likely to be in the healthiest stage (stage 1) and more likely to be in the more advanced stage (stage 3). More progress needs to be made among black and Hispanic PLWH to reduce racial disparities in stage of HIV infection.¹⁵

We found that younger PLWH were more likely to be in a healthier stage, despite lower viral suppression in this population,^5,13 probably because younger PLWH were more likely to have been recently infected and would therefore not be severely immunocompromised.

Among all transmission risk groups, persons with perinatal transmission risk had the lowest proportion (47.2%) in stage 1 and the highest proportion (20.6%) in stage 3. The less healthy stage among many persons with perinatal transmission risk may be ascribed in part to: (1) damage to their immune system caused by lifetime HIV infection, and (2) lower rates of viral suppression due to fewer treatment options and possibly lower treatment adherence, a common finding among young people.^16,17

The analysis has 1 primary limitation. The revised CDC staging system classifies stage 3 based on CD4 count less than 200 cells/mm³ or a stage 3–defining opportunistic illness. Because HIV surveillance programs regularly collect opportunistic illness information for persons newly diagnosed with HIV, but not for PLWH, the stages of HIV infection among PLWH were classified solely based on CD4 values. By doing this, the proportion of PLWH in stage 3 may be underestimated, because a PLWH with a stage-3–defining opportunistic illness could be misclassified as stage 1 or stage 2 if his/her CD4 count was 200 cells/mm³ or greater. However, the underestimation is likely to be minimal because the incidence and prevalence of opportunistic illness have dropped dramatically in the United States since the introduction of highly active antiretroviral treatment in mid-1990s, and, most importantly, few opportunistic illnesses occur in PLWH with CD4 of 200 cells/mm³ or greater.^18,19 Moreover, the staging system is intended for HIV surveillance at the population level and not for clinical management at the individual level. For this purpose, it is appropriate to use the information that is available in the HIV surveillance system to classify PLWH.¹

In conclusion, the revised CDC staging system of HIV infection is a useful tool with which to classify PLWH. Monitoring the stages of PLWH can help identify the gaps in HIV care and treatment, guide HIV intervention efforts, and allocate resources. Stage of HIV infection should be included in national and local HIV/AIDS strategies as an indicator of population-level HIV care and treatment.^12,20–26