Risk of HIV Transmission from Ordinary Spitting
There is essentially no risk of HIV transmission from ordinary spitting—saliva that is not visibly contaminated with blood poses a negligible to zero risk for HIV transmission.
Evidence-Based Risk Assessment
Saliva Without Blood: No Transmission Risk
Feces, nasal secretions, saliva, sputum, sweat, tears, urine, and vomitus are not considered potentially infectious unless they are visibly bloody; the risk for transmission of HIV infection from these fluids and materials is low 1
In the absence of visible blood in the saliva, exposure to saliva from a person infected with HIV is not considered a risk for HIV transmission 1
Exposure to saliva does not require postexposure follow-up or prophylaxis 1
Why Saliva Is Protective Against HIV
The oral cavity has multiple mechanisms that make it an extremely uncommon transmission route:
Saliva contains HIV in much lower titers than blood and constitutes a negligible exposure risk 1
Saliva rapidly disrupts 90% or more of blood mononuclear leukocytes (the cells that carry HIV), resulting in a 10,000-fold or higher inhibition of HIV multiplication 2
The hypotonic nature of saliva lyses infected cells, preventing virus multiplication and cell-to-cell transmission 2
Saliva contains endogenous antiviral factors including secretory leukocyte protease inhibitor (SLPI), lysozyme, defensins, and thrombospondin that inhibit HIV infectivity 3, 4
Physical entrapment of HIV by high-molecular-weight molecules like mucins further reduces infectivity 3
Documented Transmission Cases
Spitting: Zero Confirmed Cases
A systematic review found no reported cases of HIV transmission related to spitting 5
There is no risk of transmitting HIV through spitting 5
Biting: Extremely Rare and Context-Specific
HIV transmission by biting has been reported rarely, with only 9 cases identified in the literature 1, 5
Of these 9 cases, only 4 were classified as highly plausible or confirmed transmission 5
The majority occurred between family members (6 of 9), in fights involving serious wounds (3 of 9), or to untrained first-aiders placing fingers in the mouth during seizures (2 of 9) 5
None of the documented cases related to emergency workers and none occurred in the UK 5
Transmission through biting requires saliva contaminated with infected blood, which poses a substantial exposure risk—not ordinary saliva 1
Clinical Management Implications
No Prophylaxis Required
Post-exposure prophylaxis (PEP) is not indicated after exposure to ordinary saliva or after a bite in all but exceptional circumstances 5
Only saliva visibly contaminated with blood would warrant clinical evaluation for potential PEP 1
Contrast with Actual Risk Exposures
For perspective on real HIV transmission risks:
- Percutaneous needle injury with HIV-infected blood: 0.3% risk 1
- Mucous membrane exposure to HIV-infected blood: 0.09% risk 1
- Receptive anal intercourse: 0.5-3% per-act risk 6
- Ordinary spitting: No documented risk 5
Common Pitfalls to Avoid
Do not confuse ordinary saliva with blood-contaminated saliva—only the latter poses any theoretical risk 1
Do not initiate PEP for spitting incidents, as this exposes patients to unnecessary medication side effects without benefit 5
Recognize that the perceived threat of HIV transmission through spitting is not supported by medical evidence and should not drive clinical or policy decisions 5