People coinfected with both HIV and hepatitis C virus (HCV) have double the risk of developing an AIDS defining illness (ADI) as people infected with only HIV, according to a study published online July 10 in Clinical Infectious Diseases.

Numerous studies have demonstrated that HIV greatly accelerates HCV disease progression. It is a lot less clear, however, what impact HCV has on HIV disease progression. Studies have been mixed. Few studies have looked at the potential for an increased risk of developing an ADI in coinfected people.

To determine the risk of ADIs in coinfected individuals, Antonella d’Arminio, MD, at the University of Milan, and her colleagues examined the medical records of 5,397 HIV-positive patients in the ICONA Foundation Study Cohort. Most of the patients enrolled in the cohort in 1998, but some were enrolled as recently as 2008. Of those patients, 2,421 were also infected with HCV, and 2,976 were not. The average CD4 count was 418 in the coinfected group and 458 in the group without HCV infection. Roughly one third were women.

There were 496 ADIs in the two groups. The rate of developing an ADI was two-fold higher in the coinfected group, after adjusting for other risk factors. The rate of ADIs was three times as high for developing fungal infections, wasting, dementia and bacterial infections such as tuberculosis and Mycobacterium avium complex (MAC). People taking antiretroviral (ARV) therapy were less likely to develop an ADI than people not taking ARV therapy. People with more severely damaged livers (cirrhosis) were also more likely to have an ADI.

The authors conclude that coinfected people should be more carefully monitored for AIDS defining illnesses.