"Safety" - somebody clarify this for me

Hi Weedy,probably as you'd expect, there's a simple and complex answer to your query. The simple answer is that, ALL OTHER THINGS BEING EQUAL, the short heat up time will increase the numbers of bacteria ie the risk is increased but probably not measurably so. Within the (extended) 'danger zone' bacteria growth rate is generally proportional to temperature.

There are some assumptions in the above, including, whether the meat is single piece (less risk) or minced (more risk), the provenance of the meat, how the meat has been stored/processed.

For a more complex answer I suggest you look at Douglas Baldwin's website

http://douglasbaldwin.com/sous-vide.html

which has a good scientifically based explanation of the food hygiene issues.

As TonyB said, there's a lot of different variables that go into food safety and the Baldwin link has good information on it.

In general though, for beef and fish, the main food safety issue is where the meat came from, the quality of it, and how it was treated.

Was that piece of fish caught a week ago, sitting on ice while it's been shipped around the country, and then a few days in the supermarket shelf? Or was it caught that day and delivered to the fish market for you to eat that night?

And the thing to remember with beef is that the harmful bacteria (at least most of them) can't penetrate an intact muscle. This is why traditionally cooked rare to medium rare steaks are just fine to eat, because the outside of the muscle is seared, killing all pathogens.

Hopefully this helps some!

so would searing after sousvide cooking accomplish the same thing?

Yup, that's correct.