Incidence of resistance over time (2001–'06) based on data of a Portuguese resistance database. 2a: Multidrug resistance (MDR): at most 1 susceptible drug available over all classes. A Poisson regression model was fitted on the data (trend line) that showed a significant decreasing trend (OR = 0.82, 95%-CI: 0.72 – 0.94; P = 0.004). 2b: NRTI-, NNRTI- and PI- full class resistance (FCR): no susceptible drugs in that class available. Significant Poisson regression models were fitted on the data (trend lines).