Survival of drying. Survival at temperatures higher than 37 C. 4. Survival at temperatures lower than 37 C. 5. Starvation in the above environments. Some of them must learn to grow successfully in an alternate host, such as an insect.
Dirty hands are particularly useful in that respect.
In one of the underdeveloped countries, a high correlation was noted between diarrhea of all sorts and infestation of pediatric patients with Enterobius vermicularis. On closer scrutiny, the correlation was highest in those patients who complained of perianal itching as a result of the Enterobius. Since hand washing is not common in that country, the interpretation was that anal scratching increased the possibility of an anal-oral route for transmission of all fecal microbes. Indoor plumbing and a safe water supply are two of the absolutely essential hallmarks of civilization. Modern sewage disposal and modern water treatment have probably saved more lives than all the doctors that ever lived.