How long post SHTF before a city is safe to re enter?

[NorthernRaider]

(15 October 2012, 21:58)Ghost Wrote: It has often been mentioned that all cities will become a necropolis after TSHTF and it is for this reason that many of us are prepared to bug out. But it is likely that many of us will also need to scavenge these cities when our preps begin to dwindle.
My question is this.

How long should you wait before it is safe to re enter a city? How can you be sure that diseases like cholera and typhoid have run their course and died out?

I am of the impression that a year or at least a harsh winter will clear the city of disease. Am I right or wrong?

I was taught THREE years , cos first its the initial die off, then the inevitable disease outbreaks among survivors, the second die off then the plague of vermin and pestilance that follows until all the " edible" material is going and the rodent population falls again.