Background: A novel pandemic influenza A(H1N1) virus was isolated in 2009. Considering that individuals infected by HIV are acknowledged as vulnerable populations during an influenza pandemic, the current study was aimed at analyzing the impact of H1N1 infection in the HIV-infected population.

Methods: Procedures included a medical history, physical examination, routine laboratory tests, cultures from body fluids, bronchoscopy with bronchoalveolar lavage, imaging studies and nasopharyngeal swabs. Infection by 2009 H1N1 was assessed by RT-PCR. ORs, Fisher´s exact test and Wilcoxon’s rank sum tests were used to evaluate effects.

Results: Of 22 HIV+ and 2009 A(H1N1)+ patients (2 Female, median age 34), 12 required hospitalization, 7 required mechanical ventilation (MV), and 5 died. Median time from onset was 11 days (IQR 4-15), compared to the reported 6 days in non-HIV+ population seen at our institution. Sequential samples taken at different intervals after 5 days with 75 mg oseltamivir treatment revealed that 3/5 patients had detectable virus shedding at day 7, and 1/10 at day 11, confirmed by RT-PCR. 11 patients were on successful HAART at symptoms onset, which reduced the probability of MV (OR=0.09, p=0.03) and hospitalization (OR=0.1, p=0.03). Having an opportunistic infection raised the probability of requiring hospitalization (OR>24.5, p=0.0004), MV (OR=19.7, p=0.007), and having a longer time from onset (p=0.0008). CD4+ cell counts of all patients had a median of 155 (IQR 57-394), and hospitalized patients had a lower count (p=0.015). Patients with CD4+ counts under 200 had a higher median time from onset of symptoms to hospital valuation (15 days) than those with higher counts (7 days, p=0.046).

Conclusions: The evolution period of influenza disease in HIV-infected subjects was extended when compared with previous reports in non HIV-infected subjects, and appears to be associated with CD4+ counts. Shedding of influenza virus in some HIV-infected subjects remained even after 5 days of treatment with oseltamivir. This is relevant since persistent viral replication after antiviral therapy has been linked to the risk of emergence of resistance. The presence of OIs suggests a more complicated course of the disease as indicated by a higher number of patients in need of hospitalization, mechanical ventilation, and longer time from onset. HAART appears to have a protective effect on the severity of the disease.