Coupon Accepted Successfully!


Sexual Transmission

  1. HIV is predominantly a sexually transmitted disease.
  2. HIV is transmitted by both homosexual and heterosexual contact
  3. Most common mode of infection, world wide is heterosexual transmission.
  4. Male to female transmission is usually more efficient that female to male transmission  
Cofactors affecting heterosexual HIV transmission
  1. Presence of other STDs
    1. Strongly associated with HIV transmission.
    2. Close association between genital ulcerations and transmission - e.g. Treponema pallidum, Haemophilus ducreyi and herpes simplex virus are important causes of genital ulcerations linked to transmission of HIV.
    3. Pathogens responsible for nonulcerative inflammatory STDs are also associated with an increased risk of transmission of HIV infection e.g. Chlamydia trachomatis, Neisseria gonorrhoeae and Trichomonas vaginalis.
  2. Level of Plasma Viremia
    1. In many studies, the chief predictor of heterosexual transmission is level of plasma viremia.
    2. The rate of HIV transmission per coital act was highest during the early stage of HIV infection when plasma HIV RNA levels are highest and in advanced disease as the viral set point increases.
  3. Male Circumcision. (18th edition, Harrison)
    1. Associated with a lower risk of HIV infection among men.
  4. Use of Oral Contraceptives (18th edition, Harrison)
    1. In some studies, use of oral contraceptives was associated with an increase incidence of HIV infection
    2. May be due to drug-induced changes in cervical mucosa, rendering it more vulnerable to penetration by virus
  5. Age of Onset of sexual activity
    1. Adolescent girls might be more susceptible to infection upon exposure due to properties of an immature genital tract with Increased cervical atopy or exposed columnar epithelium.
  6. Alcohol and illicit drug use
    1. They are associated with unsafe sexual behaviors, both homosexual and heterosexual, and thus lead to increased risk of sexual transmission of HIV.

Transmission by blood and blood products

  1. Blood product
    1. Capable of transmitting HIV transmission
      1. Whole blood, packed RBC’s, Platelets, 
      2. Leukocytes, plasma concentrates of clotting vaccine
      3. Factors
    2. Not associated with HIV (hormone) (PNQ)
      1. Hyperimmune y globulin
      2. HB immune globulin, plasma derived
      3. Plasma derived hepatitis B
      4. Rho immune globulin
        1. Parenteral transmission of HIV does not require i.v. puncture; subcutaneous and intramuscular injections can transmit HIV as well. 
        2. Measures to decrease the risk of HIV transmission by transfused blood or blood products
          1) Screening of all blood for HIV nucleic acid, p 24 antigen and/or anti-HIV antibodies
          2) Self - deferral of donors on basis of risk behavior
          3) Screening out HIV -negative individuals with positive surrogate laboratory parameters of HIV infection such as hepatitis B & C.
          4) Serology testing for syphilis:
          5) Heat treatment of clotting factor concentrates
        3. Despite best effort, the risk of transfusion - related transmission of HIV cannot be completely eliminated since we cannot detect HIV RNA for the first 1-2 weeks following infection due to low levels of viremia. 
  2. Transmission by transplanted tissue and semen used in artificial insemination can occur.  This requires proper screening of organ prior to transplantation.
    In HIV sero- discordant couples (male, HIV infected; female - uninfected) who wish to conceive a child, assisted reproductive techniques using sperm washing can decrease the risk of HIV transmission. 
  3. Transmission in i.v. drug user (IDUs)

Occupational transmission of HIV

Occupational transmission of HIV - health care workers, lab workers and health care setting.
Occupational transmission of HIV can be considered to involve
  1. Transmission to health care worker and laboratory from a health care personnel who work with HIV-containing few materials (small but definite risk)
  2. Transmission of infection worker to patients (very instance) 
Exposures that place health care workers at potential risk of HIV
Exposure Risk
Percutaneous injuries (eg. needle stick I cut with a sharp object) -  0.3%
Contact of mucous membrane with blood, tissue or other potentially infectious body fluid 0.09%
Contact of nonintact skin (eg. exposed skin that is chapped, abraded or afflicted with dermatitis) mucous exposure Risk less than the risk for membrane
  • Transmission through intact skin has not been documented
Factors associated with increased risk for HIV infection
  1. Following percutaneous exposure - Increased risk is associated with exposure to relatively large
  2. quantity of blood as
    1. In case of a device visibly contaminated with patients blood
    2. A procedure that involves a needle placed directly in a vein or artery
    3. A deep injury
  3. Following mucocutaneous exposure-
    1. Exposure to an unusually large volume of blood
    2. Prolonged contact
    3. Potential portal of entry
  4. Exposure to blood from patients with advanced stage disease
    1. Owing to high titre of HIV in blood
    2. Presence of more virulent strains of virus
  • HIV containing material - Different body fluids have different potential for HIV transmission. Accordingly, they can be-classified as
Highest risk Fluids considered potentially-infectious (but risk much lower than blood exposure and not commonly implicated in occupational exposure) Fluid not considered potentially infectious unless visibly bloody
Blood and visible bloody body fluids CSF, synovial- fluid, pleural fluid, peritoneal fluid, pericardial fluid, amniotic fluid Feces, nasal secretions, saliva sputum, sweat, tears, urine, vomitus

Use of antiretroviral drugs as post- exposure prophylaxis decrease the risk of infection.

Fetal / infant transmission

  1. HIV transmission from an infected mother to her fetus can occur at various stage
During pregnancy Perinatal period Breast feeding
23-30% of cases Most common period (!50-60%) 12-20%
Can occur as early as 1st and 2nd trimester    
  1. Overall, probability of transmission ~f HIY from mother to fetus (in absence of prophylactic ART) is
    1. 15- 25 % in industrialized countries
    2. 25-35 % in developing countries .
  2. Factors associated with higher rates of transmission
    1. High maternal levels of plasma viremia-
      Best documented factor associated with higher risk of transmission. The risk
      i. Increases steadily as the level of maternal plasma viremia increases
      There may be no lower "threshold" below which transmission never occurs
    2. Low maternal CD4+ T cell count
      Low CD 4+ T cell counts are often associated with high levels of plasma viremia
    3. Closer HLA- match between mother and child
    4. Factor important for transmission during labor or perinatal period  (PNQ)
    5. Prolonged interval between membrane rupture and delivery. 
    6. Factors associated with increased mother to child transmission via breast feeding Detectable level of HIV in breast milk
      1. Presence of mastitis
      2. Low maternal CD4+ T cell counts
      3. Maternal vitamin A Deficiency        
      4. Higher risk in early months of breast feeding
      5. Mixed feeding - higher risk than exclusive breast feeding
    7. Conditions associated with potential risk, but not consistently demonstrated presence of chorioamnionitis at delivery, STDs during pregnancy, hard drug use during pregnancy, cigarette smoking, preterm delivery and obstetrical procedures as amniocentesis, amnioscopy, fetal scalp electrodes and episiotomy.
Guidelines for decreasing maternal-fetal Transmission
  1. Use of ART
Ideally, following Guidelines should be used

For mother who requires Therapy for her HIV infection    

For mother who dose not require therapy for her HIV infection

Combination therapy for mother during

pregnancy through delivery


Prophylaxis for infant

Antiretroviral prophylaxis with one or more drugs


Prophylaxis for infant

  1. In developing countries, if above regimens cannot be used, short course prophylactic ARV regimens can be used
  2. Rate of mother to child transmission is approaching <1% in pregnant women receiving combination ART.
  1. Obstetric Management
    1. Combination ARV combined with cesarean section delivery, significantly decreases risk of maternal - fetal transmission  
  2. Breast Feeding
    1. In developed countries - avoidance of breast feeding by infected mother
    2. In some developing countries~ breast milk is the only source of adequate nutrition as well as immunity for infant. The optimal approach is to provide continual treatment to infected mother who breast feed their infant. Also, intermittent administration of nevirapine to the uninfected babies is being tried. 

Mode or transmission

Risk of Transmission

Contribution to the total number of cases

Sexual transmission



Mother to child transmission



Blood transfusion



Infected syringes and needles – IDU

0.5 – 1.0



Window period : The timeframe between when a person is exposed to HIV to the time the person is tested positive for HIV antibodies. 
  1. Antibody detection - 22 days  
  2. P24 Ag detection - 16 days (LQ 2012)
  3. Nucleic acid testing - 12 days
  1. ELISA - Standard blood screening test for HIV infection
    1. Usually detects both HIV - 1 and HIV - 2
    2. Sensitivity > 99.5% ; Specificity - not optimal
    3. Factors associated with false positive ELISA - antibodies to class II antigens, autoantibodies, hepatic disease, recent influenza vaccination and acute viral infection.
    4. Reverting of a positive ELISA to a negative ELISA on treatment does not indicate clearing of infection; rather it signifies levels of ongoing exposure to virus insufficient to maintain a measurable antibody response.
  2. Western Blot - Most commonly used confirmatory test (Highly specific)
    1. Positive western blot - FDA criteria (1993) - Antibodies to 2 of the 3 HIV proteins: p24, gp41 and gp120/160.
    2. Antibody band to pol gene product p31 should also be checked to rule out false positive.
    3. Negative western bolt - is one in- which no bands are present at molecular weights corresponding to HIV gene products.                 
    4. Western bolt patterns of reactivity that do not fall into the positive or negative categories are considered "indeterminate"
    5. Causes - early HIV -1, HIV -2, pregnancy, antibodies that cross react with proteins of HIV ego antibodies that react with p24 and/or p55.
    6. For indeterminate cases -
      1. Repeat western blot after I month
      2. Attempt to confirm a diagnosis of HIV with
        1. P 24 antigen capture assay.
        2. One of-the tests for HIV RNA
  3. p24 antigen capture assay
    1. ELISA or EIA = type assay
    2. Positive in maximum upto 50% patients
    3. Greatest use - Screening test for HIV infection during suspected acute HIV syndrome 
  4. HIV – RNA testing
    1. Very useful in settings where anti - HIV antibodies may be misleading
    2. Acute infection
    3. Neonatal infection





Target amplification

Reliable to 40 copies /ml of HIVRNA


Signal amplification

Reliable to 50 copies/ml of HIVRNA


Lab Monitoring of Patients with HIV infection
  1. CD 4+ T cell Counts
    1. Best indicator of the immediate state of immunologic competence of the patient with HIV infection
    2. Measurement made either
    3. Directly or as
    4. Product of the percent of CD4+ T cells and 1'0tallymphocyte count
    5. Testing should be done at time of diagnosis and then every 3-6 months thereafter
    6. Practical use of CD4+ T cell count -
      1. If CD4+ Tee count < 350/ml- Indication for initiating ARV therapy
      2. Decline in CD4+ T cell count> 25% - Indication for change in therapy
      3. If CD4+ T cell count falls to < 200/ml - Start regimen for P. jiroveci prophylaxis (LQ 2012)
      4. If count < 50/ml- Start primary prophylaxis for MAC
  2. HIV RNA determinations
    1. By different techniques (as discussed earlier)
    2. Measurements of change in HIV RNA levels over time important for
      1. Assessing rate of disease progression
      2. Rate of viral turnover
      3. Relationship between immune system activation and viral replication
      4. Assessing time to development of drug resistance
    3. Decisions based upon HIV RNA level should never be made on a single determination as they may fluctuate greatly in setting of secondary infections or immunization.
    4. Measurement of plasma HIV RNA levels should be made at time of diagnosis and every 3-6 months thereafter in untreated patients.
  3. HIV resistance testing
    1. Done through - genotypic assays and phenotypic assays
    2. They enhances short term ability to decrease viral load by 0.5 log compared to changing drugs merely on the basis of drug history.
    3. Useful for
      1. Selection of new drugs in patients with virological failure
      2. Selecting an initial regimen
  4. Co-Receptor Tropism Assays.  
    1. Important when treatment with CCR5 antagonist is planned
    2. Usually done using a phenotypic assay  
Extra Edge:

Even though HIV causes immune suppression, it causes hypergammaglobulinemia rather than hypogammaglobulinemia. (LQ 2012)

  1. Increased p24 antibody: basis for detection in window period.
  2. T cell anergy is commonly seen in HIV
  3. Abnormal response of T cells to mitogens is a test used in HIV.

Test Your Skills Now!
Take a Quiz now
Reviewer Name