Which items are direct economic costs associated with STIs?

Direct economic costs are the out-of-pocket or market-valued expenditures directly tied to diagnosis, treatment, and medical services. From your list, the direct economic costs are:

• paying for antibiotics required for treatment
• paying for doctor visits associated with treatment
• handling the costs of an STI screening

The others are indirect costs (managing pain is a health burden, becoming less productive and missing work are productivity losses).