Müller V, Maggiolo F, Suter F et al. PLoS Pathog 2009;5:e1000454.
In this study in which established methodologies were used to investigate time trends within the Italian HIV epidemic, the results were consistent with increased virulence over time. However, since clinical virulence is affected by a combination of viral and host factors, a significant effect of the latter could not be excluded.
It remains unanswered as to whether HIV, a relatively recent human pathogen that “jumped” species less than a century ago, is continuing to adapt to its new host, thereby potentially altering its own ability to cause disease. In the current study by Müller et al., a methodology previously developed and used in the SHCS (Swiss HIV Cohort Study)  was used in the similar-sized Italian MASTER (Management Standardizzato di Terapia Antiretrovirale) cohort to evaluate clinical virulence. Clinical virulence was characterized by the decline slope of CD4+ cell counts (n=1423) and the viral set-point (the magnitude of virus load in the blood after the resolution of primary infection; n=785) in untreated patients with sufficient data points using linear regression models to detect correlation between the date of diagnosis (1984–2006) and virulence markers, controlling for age, gender, exposure category, and CD4+ cell count at entry.