Sewage Backups
from waste lines or flooding that involves sewage or river water with a heavy load of organic material carry a serious health threat. Biocides are applied as a policy to reduce potential infection. The severity depends on the content of the sewage, degree and extent of penetration of materials, the materials porosity and the contact time. The goal in these types of damages is to achieve sanitary conditions (not sterile conditions). Because of the potential health hazards from a sewage backup you must assume the worst and treat it as such.
Common sources of sewage are:
Main Line Sewage Backups
are always considered Category 3 (Black Water, Sewage Contaminated) and must be treated as such. Extract excess sewage water, treat affected non-porous material such as wood substrate, concrete with an Antimicrobial to disinfect it. The porous materials like Carpet, Pad and Drywall must be cut out and removed when ever possible.
Toilet Overflow
is water that comes from the toilet bowl. There are two categories of water that can come from this source. There is a P-Trap (a "p" shaped piece of pipe under the toilet between the sewage pipe and the toilet) if the water flows from the sewage pipe side of the P-Trap that is considered sewage water and we must assume the worst and disinfect all hard surfaces and remove any porous material it touched like Carpet, Pad, Drywall.
If the water flows from the tank into the bowl and over flows, this is considered clean water (assuming there was no urine of feces in the bowl before the overflow) and all wet material can be dried in place.
Washing Machine and Dishwasher
overflows for the most part are considered Category 2 or Gray Water . It is less hazardous than Black Water but because of the Detergents that are probably in the water you must take some precautions. If the water saturates carpet and pad the pad must be removed but the carpet can be dried and cleaned.
There are many Organisms in Sewage that can harm or kill humans. If you would like to read more about them, their names and the conditions they cause here is a link.
http://en.wikipedia.org/wiki/Sewage