Fig 4. POC-RD alone cannot reverse selection on cost-free pneumococcal resistance.

The minimal cost of resistance ($f_1^{*}$) that allows universal treatment without causing an increase in strain 1 resistance is plotted (contour lines) against the expected duration of carriage. Two POC-RD scenarios are shown: with ($Z_1^I=0$) and without ($Z_1^I=1$) transmission control. Arrows on the x axis are serotype-specific mean carriage duration estimates from [35] (serotypes with ≥15 recorded carriage episodes only). The remaining parameters (rates per day) are d = 0.001, ${\varphi }_1^C$ = 5 × 10⁻⁴, ${\varphi }_2^C$ = 0, ${\gamma }_1^I={\gamma }_2^I$ = 1, ${\gamma }_0^I$ = 0.125. We make the simplifying assumption that baseline carriage and infection transmission rates are identical (β^C = β^I = β) which ensures that $f_1^{*}$ does not depend on β. Details on parameterization are in S1G Text. POC-RD, point-of-care resistance diagnostics.