gms | German Medical Science

Although infectious diseases are commonly studied in isolation, many different diseases can be transmitted through the same contagion routes. Thus, interventions aiming to curb the spread of one might affect the incidence and endemic levels of others. One example is the case of human immunodeficiency viruses (HIV) after the introduction of Pre-Exposure Prophylaxis (PrEP) in the context of other curable sexually transmitted infections (STIs). Although PrEP has been implemented as a preventive measure for HIV infection, the transmission of other STIs has to be controlled with regular testing. This led to a new PrEP-mediated endemic equilibrium, which depended on PrEP adherence and testing behavior. What would be the effects of a shortage in PrEP supply, as observed in Germany in the last quarter of 2023? Here, we analyze the effect that a shortage in PrEP would have on the endemic equilibrium of HIV and curable STIs. We explore the possible dynamical regimes and their sensitivity in a wide parameter range, accounting for uncertainties in possible behavioral responses following PrEP shortage. We also explore the testing rates required for PrEP introduction not to induce an increase in the ground truth endemic levels of curable STIs, i.e., the parameter ranges for which an increase in the observed incidence of curable STIs would be only a testing artifact. We thereby highlight the method's potential for use combined with data and behavioral epidemiology expertise.

The authors declare that they have no competing interests.

The authors declare that an ethics committee vote is not required.