Differential Diagnosis

Single Most Likely Diagnosis

• Acute Pharyngitis or Tonsillitis: The symptoms of swollen tonsils with white spots or patches and bilateral neck lymphadenopathy, which resolved within 6-7 days, are consistent with a viral or bacterial pharyngitis. The subsequent decrease in neck lymphadenopathy and the current mild swelling and jugulodigastric lymphadenopathy could be part of the recovery process or a residual effect.

Other Likely Diagnoses

• Reactive Lymphadenopathy: This could be a reaction to the sexual exposure or the needle prick injury, even if the HIV tests are negative. The body might still react to the perceived infection or trauma.
• Other Viral Infections: Such as infectious mononucleosis (mono) caused by Epstein-Barr virus (EBV), cytomegalovirus (CMV), or other viral infections that can cause similar symptoms.

Do Not Miss Diagnoses

• HIV Infection: Despite the negative 4th generation ELISA tests, it's crucial not to miss an early HIV infection. The window period for HIV infection can vary, and while the tests are highly sensitive, there's a small chance of a false negative, especially if the infection is very recent.
• Other Bloodborne Pathogens: From the needle prick injury, such as hepatitis B or C, which have different window periods and require separate testing.

Rare Diagnoses

• Syphilis or Other Sexually Transmitted Infections (STIs): Although less likely given the symptoms, syphilis or other STIs could cause lymphadenopathy and should be considered, especially given the sexual exposure history.
• Toxoplasmosis or Other Opportunistic Infections: If the individual were to be immunocompromised (which seems unlikely given the negative HIV tests but should be considered in a differential diagnosis), toxoplasmosis or other opportunistic infections could be a possibility.

Justification and Recommendations

Given the negative 4th generation ELISA tests for HIV, the likelihood of HIV infection is low, but not zero. The symptoms presented could be consistent with an acute infection or a reactive process.

• Chance of having been infected with HIV: Low, given the negative tests, but the possibility cannot be entirely ruled out without further testing or observation.
• Chance of false negative reports: Very low with 4th generation tests, but it depends on the timing of the tests relative to the exposure.
• Chance of getting a positive result in the future: Low, but if the exposure occurred very recently, there's a small chance that the infection could still be in its early stages.
• Need of any further investigations: Yes, to rule out other causes of the symptoms, such as other viral infections, STIs, or to confirm the absence of HIV infection at a later date if necessary.
• Need of HIV NAT test or HIV 1 qualitative RNA test: Could be considered if there's a high suspicion of very early HIV infection and the 4th generation tests are negative, but generally, these tests are not the first line for routine HIV screening.