HIV Transmission Risk Calculator
This calculator provides an estimated risk of HIV transmission based on common exposure scenarios. It is not a substitute for professional medical advice. Consult a healthcare provider for accurate assessment and guidance.
Needle Stick Injury (Healthcare)
Unprotected Sexual Intercourse (Vaginal/Anal)
Protected Sexual Intercourse (Condom Use)
Blood Splash onto Mucous Membrane
Blood Contact with Non-Intact Skin
Known HIV Positive
Unknown
Known HIV Negative
Yes (undetectable viral load)
No
Unknown
Please input your exposure details to calculate risk.
Understanding HIV Transmission Risk
The risk of transmitting or contracting Human Immunodeficiency Virus (HIV) varies significantly depending on the type of exposure, the viral load of the source individual, and preventive measures taken. This calculator is designed to provide a general estimation of transmission risk for common scenarios. It is crucial to remember that this tool is for informational purposes only and does not replace professional medical consultation.
Factors Influencing Transmission Risk
- Type of Exposure: Certain activities carry higher risks than others. Invasive procedures like needle sticks have a more direct route into the bloodstream compared to skin exposure. Sexual transmission risk is influenced by the nature of the sexual act (anal sex generally carries a higher risk than vaginal sex, which carries a higher risk than oral sex).
- Viral Load: The amount of HIV in the blood (viral load) is a primary determinant of transmission risk. Individuals with a high viral load are more infectious. If a person with HIV is on effective Antiretroviral Therapy (ART) and has achieved an undetectable viral load, the risk of sexual transmission is effectively zero (U=U: Undetectable = Untransmittable).
- Presence of Other Sexually Transmitted Infections (STIs): Having an STI can increase the risk of HIV transmission during sexual contact, as inflammation and sores can provide easier entry points for the virus.
- Condom Use: Consistent and correct use of condoms dramatically reduces the risk of sexual transmission of HIV.
- Source Individual's Status: Knowing the HIV status of the source individual or partner is critical. If the source is known to be HIV negative, the risk is zero.
- Healthcare Exposure Specifics: For needle-stick injuries in healthcare settings, the depth of the puncture, the type of needle (e.g., hollow bore vs. solid), and whether the needle was visibly contaminated with blood are important factors.
How the Calculator Works (Simplified Logic)
This calculator assigns baseline risk percentages to different exposure types and then modifies these based on the source's HIV status and treatment. The formulas are based on general epidemiological data and simplified for ease of use. Actual clinical risk can vary.
The core idea is to start with a base risk for a specific exposure, then adjust it:
Base Risk: A percentage assigned to the exposure type (e.g., needle stick vs. unprotected sex).Status Modifier: Adjusts risk based on source's known status (e.g., positive, negative, unknown).Treatment Modifier: Significantly reduces risk if the source is on effective ART with undetectable viral load.
The calculation is a simplified representation. For instance, a needle stick injury has a baseline risk. If the source is known positive and not on ART, this risk is applied. If the source is on ART and undetectable, the risk becomes negligible. For sexual exposures, the base risk is lower, but factors like the number of partners, condom use, and presence of other STIs play a significant role in real-world scenarios, which are partially represented here.
Specific Exposure Risks (Illustrative Data – may vary)
- Needle Stick Injury (Healthcare): ~0.3% risk if source is positive. This can be reduced significantly with timely Post-Exposure Prophylaxis (PEP).
- Unprotected Anal Sex (Receptive): ~1.38% risk per act if source is positive.
- Unprotected Vaginal Sex (Receptive): ~0.08% – 0.1% risk per act if source is positive.
- Blood Splash onto Mucous Membrane: Lower risk than needle stick, potentially <0.1% if source is positive.
Important Considerations
Post-Exposure Prophylaxis (PEP): If you have had a potential exposure to HIV, especially in healthcare settings or following sexual assault, seek immediate medical attention. PEP, a course of antiretroviral medications taken as soon as possible (ideally within hours, and no later than 72 hours) after exposure, can significantly reduce the risk of infection.
U=U (Undetectable = Untransmittable): For sexual transmission, if a person living with HIV is on effective ART and maintains an undetectable viral load, they cannot transmit HIV to their sexual partners. This is a cornerstone of HIV prevention.
Testing: Regular HIV testing is recommended for individuals who may have been exposed. The timing of testing depends on the type of exposure and the type of HIV test used.
Disclaimer: This calculator uses generalized risk figures. Individual risk can be influenced by numerous factors not fully captured here. Always consult with a healthcare professional for personalized risk assessment and management.
Deep (visible blood, large bore needle)
Shallow (superficial, small bore needle)
Yes
No
`;
} else if (exposureType === "sexualUnprotected") {
htmlContent = `
Anal Sex (Receptive)
Anal Sex (Insertive)
Vaginal Sex (Receptive)
Vaginal Sex (Insertive)
Oral Sex (Unprotected)
Yes
No
Unknown
`;
} else if (exposureType === "sexualProtected") {
htmlContent = `
Yes, consistently and correctly
Yes, but inconsistently or improperly
No (considered unprotected)
Yes
No
Unknown
`;
} else if (exposureType === "bloodSplashMucousMembrane") {
htmlContent = `
Eyes
Nose
Mouth
Genitals
Large Splash / Droplets
Small Splash / Smear
`;
} else if (exposureType === "nonIntactSkin") {
htmlContent = `
Clearly Broken Skin (cut, abrasion, dermatitis)
Chapped or Dry Skin
Existing Dermatitis / Eczema
Prolonged (> 15 minutes)
Brief (< 15 minutes)
`;
}
detailsDiv.innerHTML = htmlContent;
}
function calculateRisk() {
var resultDiv = document.getElementById("result");
var exposureType = document.getElementById("exposureType").value;
var partnerStatus = document.getElementById("partnerStatus").value;
var artStatus = document.getElementById("antiretroviralTherapy").value;
var baseRisk = 0;
var riskDescription = "";
var riskLevelClass = "";
// — Base Risk Assignment —
if (exposureType === "needleStick") {
baseRisk = 0.3; // Standard figure for healthcare needle stick
var needleDepth = document.getElementById("needleDepth").value;
var needleContamination = document.getElementById("needleContamination").value;
if (needleContamination === "no") baseRisk *= 0.5; // Reduced if no visible blood
if (needleDepth === "shallow") baseRisk *= 0.7; // Reduced for shallower punctures
} else if (exposureType === "sexualUnprotected") {
var sexualActType = document.getElementById("sexualActType").value;
var stiPresence = document.getElementById("stiPresence").value;
if (sexualActType === "analReceptive") baseRisk = 1.38; // Higher risk
else if (sexualActType === "vaginalReceptive") baseRisk = 0.08; // Moderate risk
else if (sexualActType === "analInsertive" || sexualActType === "vaginalInsertive") baseRisk = 0.04; // Lower risk
else if (sexualActType === "oralUnprotected") baseRisk = 0.01; // Very low risk
if (stiPresence === "yes") baseRisk *= 2.0; // Increased risk with STIs
if (stiPresence === "unknown") baseRisk *= 1.5; // Assume potential risk
} else if (exposureType === "sexualProtected") {
var condomFailure = document.getElementById("condomFailure").value;
var stiPresenceProtected = document.getElementById("stiPresenceProtected").value;
if (condomFailure === "yesProper") {
baseRisk = 0.01; // Very low baseline if condom used correctly
} else if (condomFailure === "yesImproper") {
baseRisk = 0.05; // Increased risk if condom used improperly
} else { // No condom used (treated as unprotected for calculation)
// Re-evaluate based on sexual act type if we had it here, but for simplicity assume avg
baseRisk = 0.08; // Average unprotected risk
}
if (stiPresenceProtected === "yes") baseRisk *= 1.8;
if (stiPresenceProtected === "unknown") baseRisk *= 1.3;
} else if (exposureType === "bloodSplashMucousMembrane") {
baseRisk = 0.05; // Baseline for mucous membrane splash
var membraneType = document.getElementById("membraneType").value;
var splashAmount = document.getElementById("splashAmount").value;
if (membraneType === "eyes") baseRisk *= 1.2; // Eyes can be more susceptible
if (splashAmount === "large") baseRisk *= 1.5; // Larger volume increases risk
} else if (exposureType === "nonIntactSkin") {
baseRisk = 0.01; // Baseline for non-intact skin
var skinCondition = document.getElementById("skinCondition").value;
var skinContactDuration = document.getElementById("skinContactDuration").value;
if (skinCondition === "broken") baseRisk *= 2.0;
else if (skinCondition === "eczema") baseRisk *= 1.5;
else if (skinCondition === "chapped") baseRisk *= 1.2;
if (skinContactDuration === "prolonged") baseRisk *= 1.5;
}
// — Adjustments based on Source Status and ART —
var finalRisk = 0;
if (partnerStatus === "negative") {
finalRisk = 0;
riskDescription = "Zero risk of HIV transmission as the source/partner is known to be HIV negative.";
riskLevelClass = "result-low-risk";
} else {
if (artStatus === "yes") {
finalRisk = baseRisk * 0.05; // Significantly reduced risk if on ART and undetectable
riskDescription = "Very low risk of HIV transmission. Effective ART with an undetectable viral load makes transmission highly unlikely (U=U).";
riskLevelClass = "result-low-risk";
} else { // Source is positive and not on ART, or status is unknown
if (partnerStatus === "unknown") {
// If unknown, we conservatively assume potential positive status for risk calculation,
// but indicate the uncertainty.
finalRisk = baseRisk * 0.8; // Moderate uncertainty adjustment
riskDescription = "Estimated risk based on potential HIV positive source. Risk is significant if source is positive and untreated. Testing is crucial.";
riskLevelClass = "result-moderate-risk";
} else { // PartnerStatus is 'positive' and ART is 'no' or 'unknown'
finalRisk = baseRisk;
riskDescription = "Significant risk of HIV transmission.";
riskLevelClass = "result-high-risk";
}
}
}
// Ensure risk doesn't exceed a practical maximum (e.g., 100%) or go below zero
finalRisk = Math.max(0, Math.min(finalRisk, 100));
// Refine description based on final calculation
if (finalRisk === 0 && partnerStatus === "positive") { // Case where ART reduced risk to near zero
riskDescription = "Very low risk of HIV transmission. Effective ART with an undetectable viral load makes transmission highly unlikely (U=U).";
riskLevelClass = "result-low-risk";
} else if (finalRisk 0) {
riskDescription = "Very low risk of HIV transmission.";
riskLevelClass = "result-low-risk";
} else if (finalRisk >= 0.1 && finalRisk = 1) {
riskDescription = "High risk of HIV transmission.";
riskLevelClass = "result-high-risk";
}
// Add context about PEP and testing
if (exposureType === "needleStick" || exposureType === "sexualUnprotected" || exposureType === "bloodSplashMucousMembrane" || exposureType === "nonIntactSkin") {
if (partnerStatus !== "negative" && finalRisk > 0.01) { // Only suggest PEP if there's a non-zero risk
riskDescription += " Seek immediate medical advice regarding Post-Exposure Prophylaxis (PEP) and HIV testing.";
} else if (partnerStatus === "unknown" && finalRisk > 0.01) {
riskDescription += " Prompt HIV testing is recommended.";
}
}
resultDiv.innerHTML = parseFloat(finalRisk.toFixed(3)) + "% risk";
resultDiv.className = "result-container " + riskLevelClass; // Apply dynamic class
}
// Initialize details on page load
document.addEventListener('DOMContentLoaded', updateExposureDetails);