Fig. 1.

Estimating person days of follow-up with viral load greater than or 200 copies/ml or less for a hypothetical participant.

If both viral load measurements of a pair were 200 copies/ml or less (square A), then all intervening person-days of follow-up (PDFU) were considered to have been 200 copies/ml or less. The grey area represents the PDFU greater than 200 copies/ml. If both measurements of a pair were greater than 200 copies/ml viral load, then all intervening PDFU were considered to have been greater than 200 copies/ml. If the first viral load in the pair was 200 copies/ml or less and the second was above 200 copies/ml (square B), or vice versa (square C), we used a straight-line approximation to estimate viral loads between measurements.