October 26, 2012
A HIV-infected person's CD4 nadir prior to treatment initiation does not affect his or her risk of developing community-acquired pneumonia (CAP), according to a study presented at ID-Week 2012. Instead, prior CAP and AIDS-defining illness were found to be strongly associated with risk of CAP after treatment initiation.
Individuals living with HIV who are on antiretroviral therapy still have an increased incidence of bacterial pneumonia when compared to HIV-uninfected individuals. To explore the role of CD4 nadir in this increased risk, U.S. researchers analyzed data from the U.S. Military HIV Natural History Study, which followed HIV-infected patients from 1994 to 2011.
Lead investigator Pamela Ward-Demo, M.D., and her team analyzed data from 2,514 patients who had started antiretroviral therapy with a three-drug regimen during the study period. The median age was 34 years. About 93% were male, 43% were white and 43% were African American. The median follow-up time was 5.2 years. The participants were split up into three CD4 nadir groups: 0 to 200, 201 to 350 and greater than 350 cells/mL. There were 735, 998, and 781 participants in each group, respectively.
There were 291 cases of CAP after treatment initiation during 14,787 person-years of follow-up, which was a rate of 1.97 cases per 100 person-years. Before adjusting for confounding factors, CD4 nadir was associated with both CAP (P = .008) and AIDS diagnosis (P < .001). However, after using an adjusted model, CD4 nadir was no longer significantly associated with time to CAP.
"The number one predictor of having a CAP event after HAART initiation is having one before HAART," study co-author Octavio Mesner, M.S., said. "You're 12 times more at risk to have a CAP event after HAART initiation if you had one previously."
As to why prior infection with pneumonia was a strong predictor, Ward-Demo speculated on a few possibilities: "Maybe there was damage done to the lungs that's going to make them more predisposed. Or is HIV affecting them differently, making them more predisposed? Did the pneumonia not completely clear the first time and later on redeveloped? Maybe there's another piece that's not being captured by just looking at CD4 itself to explain that. Or is there something unique about this sub-population that's still prone to getting pneumonia, regardless of their CD4 count, that is unique among that sub-group of HIV patients and that we don't quite know yet?"
She added that these findings should encourage HIV-infected patients and providers to look beyond CD4+ cell count as a marker of immunological status, stressing that this is "another reason to tell patients to stop smoking and to address some of the other pneumonia risk factors."
Ward-Demo and her team are looking to further investigate why HIV-infected patients are more susceptible to CAP despite being on HAART and having stable CD4 counts. They plan on studying other factors, including CD4/CD8 ratios and viral load.
Warren Tong is the research editor for TheBody.com and TheBodyPRO.com.
Follow Warren on Twitter: @WarrenAtTheBody.
Reporting for this article was contributed by Myles Helfand.