This case study tells the story of “Sammy,” a freshman undergraduate student who is experiencing her first weeks on campus, in order to teach the importance of proper antibiotic usage, STD (sexually transmitted disease) screening, and prevention strategies. Sammy ends up contracting chlamydia and is prescribed a one-week treatment of the antibiotic doxycycline. However, once Sammy starts to feel better, she stops her treatment. This allows the chlamydia bacteria to proliferate, some of which are resistant to the antibiotics. The first part of the case study ties in topics such as antibiotic resistance, the theory of natural selection, and the detrimental consequences of improper antibiotic usage. The second part is optional and delves into STD screening and prevention strategies defined by the Centers for Disease Control and Prevention (CDC). Students access NCHHSTP AtlasPlus, an online interactive tool hosted by the CDC, to investigate trends and infection rates of chlamydia in their state. This case study is appropriate for advanced senior-level high school students or freshman undergraduate students with a background in general biology.