What is the diagnosis and management of a 25-year-old sexually active woman presenting with lower abdominal pain, fever, unusual vaginal discharge, dyspareunia, and intermenstrual bleeding, with cervical motion tenderness and adnexal tenderness on examination, suggestive of Pelvic Inflammatory Disease (PID)?

Pelvic Inflammatory Disease (PID): This is the most likely diagnosis given Sarah's symptoms of lower abdominal pain, fever, unusual vaginal discharge, pain during intercourse, and spotting between periods, along with cervical motion tenderness and adnexal tenderness on examination. PID is a common condition in sexually active women and is often caused by bacterial infections.

Endometriosis: This condition can cause chronic pelvic pain, dyspareunia (pain during intercourse), and irregular menstrual bleeding, which align with some of Sarah's symptoms.
Ovarian Cyst: Ovarian cysts can cause lower abdominal pain and can sometimes rupture, leading to acute pain and potentially some of the other symptoms Sarah is experiencing.
Ectopic Pregnancy: Although less likely if Sarah is using contraception, an ectopic pregnancy can present with abdominal pain, spotting, and pain during intercourse, especially if the pregnancy is ruptured.
Vaginal or Urinary Tract Infections: These infections can cause abnormal discharge and pain, but the presence of fever, cervical motion tenderness, and adnexal tenderness points more towards PID.

Ectopic Pregnancy: As mentioned, this is a critical diagnosis not to miss due to its potential for severe morbidity and mortality if not promptly treated.
Appendicitis: Although the symptoms might not perfectly align, appendicitis can sometimes present with lower abdominal pain and fever, and missing this diagnosis could lead to severe consequences.
Ovarian Torsion: This is a surgical emergency that can cause severe abdominal pain and might be considered, especially if there's a history of ovarian cysts.

Diverticulitis: While more common in older populations, diverticulitis can cause lower abdominal pain and fever, but it would be less likely in a young woman without other gastrointestinal symptoms.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic abdominal pain, fever, and irregular menstrual bleeding due to malabsorption, but they are less likely given the acute presentation and specific symptoms.
Malignancies: Ovarian or uterine cancers are rare in young women but could potentially cause some of the symptoms Sarah is experiencing, especially if there's unexplained weight loss or other systemic symptoms.

Most Likely Diagnosis: PID, due to the combination of lower abdominal pain, fever, unusual vaginal discharge, and specific findings on physical examination.
Common Causative Organisms of PID: These include Neisseria gonorrhoeae, Chlamydia trachomatis, and other bacteria that can ascend from the vagina and cervix into the upper genital tract.
Diagnostic Tests:
- Pelvic exam to assess for cervical motion tenderness and adnexal tenderness.
- Laboratory tests for gonorrhea and chlamydia.
- Complete Blood Count (CBC) to look for signs of infection.
- Imaging studies like ultrasound if an ovarian cyst, ectopic pregnancy, or other conditions are suspected.
Recommended Treatment for PID: Antibiotic regimens that cover N. gonorrhoeae, C. trachomatis, and other possible pathogens. Treatment should be started promptly, even before laboratory confirmation, if the clinical diagnosis is strongly suspected.
Potential Complications of Untreated PID: These include infertility, ectopic pregnancy, chronic pelvic pain, and increased risk of HIV transmission.
Preventive Measures:
- Safe sex practices, including the use of condoms.
- Regular screening for sexually transmitted infections (STIs) in sexually active women.
- Vaccination against human papillomavirus (HPV), which can reduce the risk of certain STIs and cervical cancer.
- Avoiding douching, which can increase the risk of PID by pushing bacteria into the upper genital tract.