According to Catholic teaching, would it be a mortal sin if a Catholic were to knowingly pass on their sickness to another person?

For example, say that a Catholic has an important project that they have been working on at their workplace and he/she is very close to finishing this project, however, he/she unfortunately comes down with the flu and so he/she needs to take time off from work to recover from the flu.

Say that this Catholic were to then decide to return to work before he/she has fully recovered from the flu, because he/she is afraid or paranoid that their project will fail due to their absence, and he/she believes that a failed project could lead to them being terminated from their job. A few days later, several of his/her coworkers come down with the flu and they have to miss work due to coming down with the flu.

Has this Catholic commited a mortal sin by knowingly passing on the flu to his/her coworkers?

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    Do we have any reason to believe it should be considered a sin? As a counterexample, until the fairly recent development of an effective vaccine, it was commonly considered a virtuous act to hold "chicken pox parties" to innoculate children against the disease early in life, through precisely the mechanism of "sick person passing it on to others" that you're asking about here.
    – Mason Wheeler
    Commented Jan 18 at 20:33
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    I think that what you describe would not be a mortal sin, especially in view of a (well-founded?) fear of being fired. It would be different if the disease were not the flu but something much more serious. It would also matter whether there was a malicious intent to infect co-workers (as opposed to merely taking an imprudent risk.) But all of this is just my opinion, and so not an answer. For a real answer, consult a trustworthy priest. Commented Jan 18 at 20:57
  • @MasonWheeler Chicken pox parties would only be attended with the permission of parents (though the will of the children probably should've been considered too.) No one would intentionally want someone to pass the flu to them! It's not a parallel situation at all.
    – curiousdannii
    Commented Jan 19 at 2:01
  • knowingly is not quite the same as intentionally. Even in the scenario given, it can't be known with sufficient certitude that the person was the "vector." Mortal sin requires more than a probability of knowledge
    – eques
    Commented Jan 19 at 16:28

1 Answer 1


Is it a mortal sin for a Catholic to knowingly pass on his/her sickness to another person?

That would depend on the gravity of the communicable disease in question.

Has a Catholic commited a mortal sin by knowingly passing on the flu to his or her coworkers?

The short answer is no. At least for what we call the common cold or flu. In fact, one is not always even aware of when one is contagious with these types of illnesses.

On the other side of the spectrum, it could very well be a mortal sin to deliberately pass on some sort of communicable disease that is considered a death sentence.

Deliberately infecting someone with HIV/AIDs, bubonic plague, ebola while one is truly contagious, would be considered a mortal sin because the gravity of the situation would be serious enough to kill someone.

But back to the common flu, it would not be considered serious enough to be raised to the level of a mortal sin. The cause could be made that one lacked prudence in not staying home while one was contagious and thus sinned venially against the virtue of prudence.

Staying home and resting when you’re sick is an important part of both getting better and preventing further spread of illness. You should avoid going back to work or school until you’re no longer contagious.

The contagious period for the flu begins about 1 day before symptoms start and can last as long as 5-7 days from when you first felt sick.

You’re generally contagious with a cold 1-2 days before your symptoms start, and you could be contagious as long as your symptoms are present—in rare cases, up to 2 weeks. - Am I Still Contagious?

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    The flu kills hundreds of thousands a year, and can be extremely serious for the elderly or the immunocompromised. And we're not always aware of who is in that category.
    – curiousdannii
    Commented Jan 19 at 2:03
  • @curiousdannii and your point? I do not have a greater responsibility for their health than they have for their own. Mortal sin requires full knowledge and consent not merely probabilistic knowledge. I would have to know that I am contagious and that I will spread it to someone to even be close to that category. A lack of consideration is more an issue of prudence but not necessarily as grave as a mortal sin per se.
    – eques
    Commented Jan 19 at 16:31

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