The higher an individual's pure-tone threshold average is, the poorer their hearing is considered to be.
The findings, published in JAMA Otolaryngology - Head and Neck Surgery, come after an evaluation of the pure-tone hearing thresholds of men and women, some with the human immunodeficiency virus (HIV+) and some without (HIV-).
HIV is a virus that impairs the immune system, making people with the condition increasingly susceptible to infection and disease. There is currently no cure, but HIV+ individuals can be given a combination of medicines called highly active antiretroviral therapy (HAART) to slow the spread of the virus.
Since HAART became widely used, there has been very little investigation into the relationship between HIV infection and hearing loss, according to the study authors.
"There have been limited data obtained on the effects of HIV-related medication use on hearing loss," they write, "and in the few published studies, it is difficult to attribute the increases in hearing loss specifically to HIV medication use rather than age or cumulative noise exposure."
Dr. Peter Torre III, of San Diego State University in California, and colleagues set out to determine whether HIV disease variables and HAART are associated with changes to pure-tone threshold levels - the softest sounds audible to individuals for the majority of the time.
Evaluating the pure-tone threshold averages
For the study, the researchers assessed the hearing of 262 men with an average age of 57 and 134 women with an average age of 48.
Of the men, 117 (44.7%) were HIV+, and of the women, 105 (78.4%) were HIV+. Participants were taken from the sites of the Multicenter AIDS Cohort Study and the Women's Interagency HIV Study.
Pure-tone threshold levels were measured in both ears in a sound-treated room. The researchers tested a wide range of frequencies, from 250 Hz to 8,000 Hz.
The researchers discovered that high- and low-frequency pure tone averages (LPTA and HPTA) were significantly higher in the better ears of the HIV+ participants, indicating that their hearing was poorer than the HIV- participants.
Even after adjusting the findings for current CD4+ cell count, HIV viral load and long-term exposure to antiretroviral medication, the results remained the same.
"To our knowledge, this is the first study to demonstrate that HIV+ individuals have poorer hearing across the frequency range after many other factors known to affect hearing have been controlled for," write the authors.
Poorer hearing also found in individuals with diabetes mellitus
"The participants were middle-aged," write the authors, "so an HIV effect on LPTA was not expected, given the speculation that long-term [HAART] exposure or HIV itself contributes to premature aging."
Although unexpected, the authors also note that hearing loss at both LPTA and HPTA has previously been observed to be more likely in adults with diabetes mellitus. "It is possible that both HIV infection and diabetes, being systemic diseases, could affect the neural function of the cochlea," they suggest.
The study is limited by the fact that participants were only recruited from specific geographical areas, namely Baltimore, MA, and Washington, DC. For women, the ratio of HIV+ to HIV- participants was also uneven, and future studies could rectify these representational imbalances.
"Although we do not understand the mechanism of hearing loss found in our study, our results suggest that HIV+ individuals may have physiologic changes that mimic other chronic conditions that affect hearing levels," conclude the authors.
Earlier this month, Medical News Today reported on a mouse study suggesting hearing loss could be prevented by a vitamin supplement that protects the nerves stimulating the cochlea.