Variance of viral load measurements.

<p>For this figure we simulated influenza virus infection in 1000 patients that all had the same natural course of infection. For each of the patients, viral load measurements were generated, simulating qPCR (upper row) and TCID₅₀ assays (lower row). The variance of the TCID₅₀ assay (lognormal distribution) is greater than that of the qPCR assay (Poisson distribution). The variance of the viral load assays is small compared to the variation in natural infection among patients. Upper row: qPCR measurements, unit: viral cDNA/ml. Lower row: TCID₅₀ measurements, unit TCID₅₀/ml. a, c: True (simulated) viral load curves of 1000 patients with same course of natural infection. b, d: simulated measurements of 1000 patients with the same natural course of infection. b: lower limit of quantification of the PCR assay was 3.33 log₁₀ cDNA/ml (2137 cDNA/ml), d: lower limit of quantification of TCID₅₀ assay was 2 log₁₀ TCID₅₀/ml (100 TCID₅₀/ml).