Friends of mine who have taken cruises consistently mention the very careful measures that cruise ships take to prevent illness among passengers. Not infrequently, entire voyages are ruined because of widespread sickness among the passengers.

It makes sense that cruise ships would be at risk for this, since there are lots of people in an enclosed space. But then I wondered, how is this not even more of a problem aboard the ISS? After all, it's a hermetically sealed place, it's difficult to bathe effectively, and based on what I've read about the toilet situation, it would be hard to keep fastidiously clean.

This question addresses communicable diseases. Basic diarrhea seems like a more run-of-the-mill type of illness; I don't know whether it would be possible to detect whether someone was going to have an incident in the next few weeks. And at that point, why wouldn't it just spread all around the station and remain an ongoing problem?

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    $\begingroup$ I'm guessing that the answer to this will center around the fact that they don't send up anyone who they even remotely suspect might be getting sick... $\endgroup$ – user Dec 14 '16 at 16:00
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    $\begingroup$ @MichaelKjörling I believe that is correct. Astronauts go through extensive medical examination, right up until they launch to the ISS, which checks for (among other things) communicable illnesses, to make sure no disease is spread. Cruise ships don't even require a bill of health from a doctor, and many also make stops in places where people are likely to pick up a contagion. $\endgroup$ – called2voyage Dec 14 '16 at 16:14
  • $\begingroup$ Adam, considering your comment about the toilet situation, you might find this post interesting (if you haven't already read it): space.stackexchange.com/q/845/58 $\endgroup$ – called2voyage Dec 14 '16 at 16:18
  • $\begingroup$ Though I can find no other mention of diarrhea in space, Borman's instance of diarrhea and vomiting on Apollo 8 was apparently later considered to be a symptom of space sickness. Since many have suffered from space sickness, it is possible that others have had diarrhea as well. $\endgroup$ – called2voyage Dec 14 '16 at 16:58

They undergo a medical examination 10 days before launch and are then quarantined. Then they are examined again 2 days before launch and again shortly before suiting up.


Diarrhea in particular is usually caused by a virus or bacterial infection, allergies, and eating foods that upset the digestive system.


Since the astronauts are thoroughly examined, the risk is substantially lowered. In addition astronauts' diet is strictly watched by NASA and the water and air are recycled in a fashion that reduces chances of contamination.

As for cruise ships, it appears that recent incidents have been linked to poor sanitation according to news reports.

  • $\begingroup$ I've removed the post notice, but I still think an explanation of space sickness is in order. $\endgroup$ – called2voyage Dec 14 '16 at 21:29
  • $\begingroup$ Is fecal matter really not a danger unless you already have bad bacteria in your system? $\endgroup$ – adam.baker Dec 15 '16 at 2:23
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    $\begingroup$ @adam.baker -- The vast majority of those cases of rampant diarrhea on cruise ships are norovirus infections. This virus is highly contagious. A simple handshake more than suffices; even touching a doorknob recently touched by an infected person will do. It also has a short incubation period of one to three days. The ten day prelaunch quarantine pretty much eliminates the possibility of the norovirus getting to the ISS. $\endgroup$ – David Hammen Dec 16 '16 at 16:24

Thousands of passengers from all over the world interacting with each other for the first time and with thousands more at every port they visit. Millions of infection vectors. Add to this the difficulty in sourcing preparing thousands of meals without a single slipup in hygiene.

Less than 10 people who were carefully screened for medical problems before flight, and who have been living in the same area and interacting with each other for years. Their immune systems are already 'used to' the other crewmembers. Very few visitors that can bring in new pathogens. Meals are prepared on a cost-no-object basis.

Other than being in a confined space, the two have little in common.


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