Sewage Testing After Clean Up

May 4, 2018

A unique service that we offer is sewage testing after clean-up.  This type of testing can be helpful when there was a sewage backup and it is unclear if the clean-up was successful.  In this blog post, I will provide some background information on sewage testing.

Disinfecting Is Not Enough

When there is a sewage backup, disinfecting surfaces is not the only step that should be taken.  Disinfectants will state that they must be used on a cleaned surface, so cleaning should be the first step of the process.  But not every surface can even be cleaned and disinfected. Porous materials such as drywall and paper materials that were impacted by the sewage should be discarded rather than treated.

Cleaning any areas that were impacted means physically removing any matter and stains from the areas affected.   Cleaning affected surfaces can be compared to washing your hands. When you wash your hands you are using soap and water to remove dirt, grease, and other visible signs of uncleanliness. Disinfecting, on the other hand, is more similar to using hand sanitizer.  Hand sanitizer does not remove physical signs of dirt and grease but it does help kill pathogens that may be present. Just as you would advise a kid to first wash his hands after playing in mud, it is important to first clean hard surfaces before disinfecting them.

Traditional Sewage Testing

How do you know if the cleaning and disinfecting worked? There are a few different methods for evaluating surfaces following a sewage cleanup.    

The traditional method used by laboratories is to screen for the presence of indicator organisms such as the total coliform, fecal coliform, E. coli, and fecal streptococcus.  This type of testing checks for viable (living) bacteria.  Unfortunately, many bacteria are anaerobic, meaning that they thrive in an oxygen-free environment and cannot survive in the presence of normal air.  The longer anaerobic bacteria are out in the open, the higher the likelihood that they will die. This means that the longer you wait to take a sample the less likely this type of testing will show the presence of bacteria. The results from this type of testing can show that there are no viable bacteria present but it would not show any dead bacteria that may still be present on affected surfaces.  

Should you even be concerned about dead bacteria? Even when some bacteria are non-viable they can still be dangerous.  Some dead bacteria can be hazardous to human health because they can have endotoxins. Endotoxins are found in the cell wall of gram-negative bacteria.  When airborne, endotoxins can cause chest tightness, cough, shortness of breath, fever, and wheezing among other health effects Olenchock S.A. Airborne Endotoxin. In Manual of Environmental Microbiology, 1st Ed.; Hurst, C. J.; Crawford, R.L.; Garland, J.L.; Lipson, D.A.; Mills, A.L. Eds.; ASM Press: Washington D.C., 1997; 661-665. .

DNA Testing

Due to the shortcomings of traditional viable testing, we often use DNA testing to determine if a sewage cleanup was successful.  This analysis method is very sensitive and can detect both viable and non-viable bacteria on surfaces making it a better option to test an area after a sewage cleanup.  This type of DNA testing analyzes swab samples using polymerase chain reaction (PCR). With PCR testing, the presence of a specific type of bacteria DNA is chosen. Bacteroides DNA is used as an indicator for the presence of fecal bacteria.   Bacteroides DNA is used because it is one of the most prevalent types of bacteria found in the gut of humans Wang, R.F.; Cao, W.W.; Cerniglia, C.E. PCR detection and quantitation of predominant anaerobic bacteria in human and animal fecal samples. Appl Environ Microbiol. 1996, 62(4), 1242–1247. . Although Bacteroides is anaerobic, it serves as a good indicator for the presence of other types of bacteria.  DNA testing is a helpful tool to use because dead bacteria is still detectable even after disinfection.  


A sewage back-up or spill is messy, gross, and potentially dangerous.  Cleaning and disinfecting the affected areas is essential, but ensuring that the clean-up was successful is also a critical part of the clean-up process.  At Indoor Science, we offer swab testing for Bacteroides post cleaning to ensure that potentially dangerous bacteria (dead or alive) are no longer present in your property.