Whilst on a recent refresher course it was highlighted that when considering risk of exposure to infection from bodily fluids we should be aware of two distinct risk levels:

High Risk:

  • Blood
  • Semen
  • Vaginal Secretions
  • Diarrhea

Low Risk:

  • Saliva
  • Vomit
  • Urine
  • CSF (Cerebrospinal fluid)

Why is it that some bodily fluids are a greater infection risk than others? Is it related to the fluids themselves or the species of pathogen that are located within them?

  • 1
    $\begingroup$ I feel like sputum / mucus should be on that list. It's the primary bodily fluid that influenza and other respiratory tract infections are spread with. $\endgroup$
    – GWW
    Commented Apr 4, 2012 at 23:42
  • 6
    $\begingroup$ Likely because the fluids on the high risk list are commonly exploited routes of viral shedding, bacterial transit, and also the likeliest to pick up other microbes on their exit from the body. Saliva is not sterile, but arguably more so than the others; vomit is highly acidic therefore inhibits microbe presence; urine can be higher risk depending on STD or UTI status; CSF is low risk probably because of the rarity of exposure. $\endgroup$
    – user560
    Commented Apr 5, 2012 at 1:03
  • 1
    $\begingroup$ @GWW Yeah it probably should - these were just mentioned specifically by the trainer :) $\endgroup$
    – Rory M
    Commented Apr 5, 2012 at 10:23
  • 1
    $\begingroup$ I would say that diarrhea is a medical condition, not a bodily fluid. I would use the term feces instead (OK, fluid does not apply to that either, maybe "bodily secretion" would be better?) $\endgroup$
    – nico
    Commented Apr 6, 2012 at 18:11
  • 2
    $\begingroup$ @Rory M: good point, although I have to say I wouldn't like to be the one who tested that!!! :D $\endgroup$
    – nico
    Commented Apr 6, 2012 at 18:15

1 Answer 1


This is just about where the pathogens can be found that are dangerous to people.

Vomit is highly acidic and less accommodating to microbe growth. Similarly saliva has many immune components in it as well as digestive enzymes that keep most microorganisms down.

Urine and CSF are actually quite sterile as they come from environments that are highly filtered - the kidney is an osmotic processor that essentially is a molecular filter and does not allow cells to pass, the spine is highly insulated from the blood and other direct exposure to microorganisms.

Compare that with the 'dangerous' list and you have organs that are open to human pathogens. Venerial disease like HPV is so common that what - about 1 in 5 people under a certain age carry it. That is a pretty high expectation of a biohazard. most infections and viruses are blood bourne - influenza, cold, as well as any bacterial infections.

Feces is always a dangerous thing to handle as the digestive tract is rich in nutrients and essentially directly open to external bacteria and fungi. (and its not acidified like the stomach). Also parasites like tape worms and other multicelled animals! yum!

Diarrhea is often caused by an infection of some sort, so its just more likely a hazard, but feces is always a place where you might find a pathogen.

This is not to say that the 'safe' list is totally safe. Its just less likely to bear disease causing agents.

  • $\begingroup$ Largely unrelated question: if roughly 1 in 5 have HPV or this venereal disease in question before a certain age, wouldn't they continue to do so after that age? Or is the mortality so high as to bring down the fraction of the (living) population that has it? Why am I not hearing about this as one would if, say, the plague were going around? $\endgroup$ Commented Oct 28, 2015 at 18:53

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