Situation: The nurse at a Rural Health Unit (RHU) provides HIV and sexually transmitted infection (STI) services, including counseling, testing, and linkage to care. A 24-year-old man had condomless sex 36 hours ago with a partner whose HIV status is unknown; the physician assesses the exposure as high risk. His HIV test today is nonreactive. What should the nurse arrange?

Post-exposure prophylaxis (PEP) must start as soon as possible and within 72 hours of exposure, and it is taken for 28 days. At 36 hours he is still within the window for PEP. Pre-exposure prophylaxis is for ongoing risk before exposure and can be discussed after PEP is completed.

Clinical context
A 24-year-old man presents 36 hours after a high-risk condomless sexual exposure. His HIV test today is nonreactive, but a nonreactive test at this point only reflects his HIV status before this exposure; it cannot rule out infection from the exposure that occurred 36 hours ago. The priority is therefore not to wait for seroconversion but to intervene while viral replication may still be interrupted.

Why PEP is the correct action
Post-exposure prophylaxis is a time-limited course of antiretroviral medication started after a potential exposure to prevent HIV acquisition. The critical principle is that PEP must be initiated as soon as possible and no later than 72 hours after exposure, and the recommended duration is 28 days ^[4]. At 36 hours, this patient remains within the eligibility window, so starting PEP today is appropriate. The nonreactive test result does not contraindicate PEP; rather, it provides baseline information and helps confirm that the patient was not already HIV-positive before this exposure.

The rationale for the 72-hour cutoff is grounded in the biology of early HIV infection. After mucosal exposure, the virus initially infects local target cells and then disseminates through regional lymph nodes over the first few days. Antiretroviral drugs are most effective when they can act before widespread systemic dissemination and establishment of latent reservoirs. Earlier initiation—ideally within 2 hours—is associated with the highest probability of preventing infection, but benefit persists up to 72 hours ^[4]. Initiating at 36 hours is therefore still clinically meaningful.

PEP versus PrEP
Pre-exposure prophylaxis is a different strategy intended for individuals with ongoing or anticipated risk; it is taken before exposure and continued during periods of risk. In this scenario, the exposure has already occurred, so PrEP is not the immediate intervention. Key point! PrEP may be discussed later—after PEP is completed—if the patient has ongoing risk, but it does not address the acute exposure that happened 36 hours ago.

Why waiting for a repeat test is unsafe
A repeat HIV test after the window period would delay any intervention until after the time when PEP could have been effective. The window period for laboratory detection of HIV can range from about 2 to 6 weeks depending on the assay, and by the time seroconversion is detectable, the opportunity for post-exposure prevention has passed. Watch out! A negative test today does not mean the patient is uninfected from this exposure; it means he was uninfected before this exposure. The decision to start PEP must be based on exposure risk and timing, not on a single early negative test.

Regimen considerations
Current guidance supports a 3-drug antiretroviral regimen for 28 days ^[4]. Updated recommendations favor coformulated regimens that include an integrase strand transfer inhibitor combined with a tenofovir and lamivudine or emtricitabine backbone, because these combinations are better tolerated and may support adherence compared with older regimens . Tolerability matters because completing the full 28-day course is essential for efficacy; regimens associated with fewer side effects are more likely to be finished.

Nursing responsibilities at the RHU
The nurse should arrange same-day initiation of PEP, provide education about the importance of completing all 28 days, and schedule follow-up HIV testing at the appropriate intervals after completion. Baseline testing for HIV, hepatitis B, hepatitis C, and renal function is typically obtained before or at the time of starting PEP. The nurse should also assess for any contraindications to specific antiretrovirals and provide counseling about safer sex practices during and after the PEP course.

Intervention	Timing	Purpose
PEP initiation	As soon as possible, within 72 hours	Interrupt early viral replication before systemic dissemination
PEP duration	28 days	Complete course required for optimal prevention
Follow-up HIV test	After PEP completion, per protocol	Confirm whether infection was prevented
PrEP discussion	After PEP, if ongoing risk	Address future prevention needs

The correct nursing action is to arrange post-exposure prophylaxis started today and continued for 28 days, because the patient is still within the 72-hour window and the exposure is assessed as high risk ^[4].