No such database exists. PubMed is simply a compilation of standard research literature -it is not a mechanism for judging study quality or reliability. The CDC database may be more reliable.
No, there is no way to know for sure. The frequency with which studies containing contrived or manipulated data (and hence wrong conclusions), or studies that fail to publish data not supporting the "desired" study hypothesis is probably MUCH larger than is known. In fact, a study was published in the 80's or 90's (I don't recall the author's name) that concluded (and this study wasn't selling any product) that easily 50% of medical research study reached conclusions NOT supported by the presented data!
So, look at any study with a certain healthy amount of skepticism, especially if that study demonstrates unexpectedly positive results compared with other studies. This is not to say that these studies should not be taken into account or, if seemingly reliable, not applied in practice but it is to say that always have a healthy eye out for the possibility that the results will be proven wrong or inapplicable.
BTW, as an aside, very few doctors understand enough about statistics to accurately evaluate studies and their conclusions - they depend on "experts" to do so and these "experts" are, unfortunately, often paid very handsomely for their "expert" advice pharmaceutical and medical equipment companies. Such "expert" opinion also has to be viewed with a certain amount of healthy skepticism.