You are advising a resource-limited clinic during an influenza season. With funds for only one major intervention, you can either (A) provide masks to ill patients (source control), (B) install improved HEPA filtration in waiting rooms (environmental transmission interruption), or (C) offer antiviral prophylaxis to all staff (prevent colonization). Which option should you recommend and why?

• A. Do nothing because any single intervention is ineffective without simultaneous mass vaccination campaigns, and advising individual clinics to pick one measure is scientifically unsound and ethically unjustifiable.
• B. Offer antiviral prophylaxis to all staff (C) since pharmacologic prevention of colonization is inexpensive and eliminates the need for any other infection-control measures among clinical personnel regardless of community transmission intensity.
• C. Install HEPA filtration (B) because environmental upgrades always outperform behavioral measures like masking in all respiratory outbreaks and will automatically protect everyone equally without requiring adherence.
• D. Provide masks to ill patients (A), because source control targets the reservoir/portal of exit immediately and is likely to reduce the greatest amount of onward transmission per dollar spent in a setting where symptomatic people are the primary source.

Answer: (D)