Implications of antibiotic use for co-infections when a fitness trade-off for resistance is present

How much does indiscriminate antibiotic use promote the spread of antibiotic-resistant infections in a population? Assuming a fitness trade-off for resistance exists, it is possible for an antibiotic-vulnerable strain to outlast a resistant type within an untreated host carrying both. That means prudent treatment schemes can potentially manage resistance levels in the population-at-large. We use a compartmental ODE model incorporating a class of coinfected individuals to analyze the epidemiology. The Next Generation Operator method gives R0 for the two strains, and we perform invasion analysis for both types under different treatment schemes. Haphazard antibiotic use favors resistant strains by treating both singly-infected and co-infected people, while shrewd treatment targets those carrying the vulnerable strain only. According to the model, inattentively treating co-infected individuals significantly promotes resistance in a population.