Even urine odor that seems to linger throughout a facility may originate in specific places. A study at one elderly care facility in Fukushima Prefecture identified sources including the bottoms of portable toilets and carpet beneath beds. After a year of cleaning and disinfection focused on those locations, local odors and staff odor ratings decreased.
The study centered not on simply placing deodorizers around the building, but on using human smell, chemical analysis, and bacterial testing to locate where odor was being generated. It reports both a method of investigating the causes and the process of translating those findings into daily work.
First, establishing what smells and where
The setting was an approximately 20-year-old geriatric health services facility. Comments about odor from residents’ families prompted staff and researchers to work together. Air purifiers were already installed, and professional carpet cleaning was already being carried out twice a year.
Staff rated odor intensity at four locations on a six-point scale from 0 to 5 and selected odor qualities such as urine, feces, and sweat, with multiple responses allowed. Urine odor was frequently reported, and the strongest ratings were for the area just before the access door on the hospital side.
A three-person expert panel, including two certified odor assessors, also surveyed the building and mapped odor intensity onto its floor plan. Odor increased along a corridor. Closer inspection of nearby rooms revealed strong urine odor and urine stains in carpet beneath beds, at the bottoms of portable toilets with urine-scale deposits, and on some bed sheets.
The starting point was to go beyond room and corridor odors and approach specific areas to locate the sources. Privacy precautions included surveying rooms while residents were absent and preventing published data from being linked to room numbers.
p-Cresol was a more useful clue than ammonia
Urine odor often brings ammonia to mind. In this study’s preliminary measurements, however, ammonia above the detector tubes’ detection limits was not measured in a pooled sample of urine from portable toilets used overnight. This finding applies to this facility and these sampling conditions.
By contrast, sampling air with sorbent tubes and analyzing it by GC/MS detected phenols, fatty acids, aldehydes, indoles, and other compounds. The concentration of p-cresol, a phenolic compound, corresponded particularly well with human odor-intensity ratings.
The correlation coefficients were 0.89 across four air-sampling locations inside and outside the facility and 0.93 across four source locations. Comparisons at so few locations cannot establish one substance as the cause of all urine odor, but p-cresol proved a useful indicator in this investigation.
For example, the p-cresol collected from a portable toilet with urine scale was about ten times that from one with almost no scale. A urine-smelling carpet area had about seven times the level of an area without urine odor. These findings connected the building-wide survey to specific contaminated locations.
Looking for bacteria involved in odor production
Urine contains precursors of odor compounds in forms that do not readily evaporate. The study focused on β-glucuronidase, an enzyme capable of breaking down such conjugated compounds. Bacteria with this enzyme activity can participate in a pathway that releases p-cresol and other compounds from urinary precursors.
The researchers cultured swab samples and counted colonies with β-glucuronidase activity by their color change. Large numbers of active bacteria were detected at the bottoms of urine-scaled portable toilets even after water rinsing. They were also present in urine-smelling areas of dry carpet and relatively dry sheets.
Sequencing representative colonies identified Escherichia coli in portable toilets, an Enterococcus species in carpet, and several other bacteria in sheets. The bacteria involved in similar urine odors may differ by location. This was an environmental investigation of odor generation, not a diagnosis of infections in residents.
A year of work tailored to the sources
Once the sources had been identified, staff incorporated cleaning and disinfection of urine-smelling carpet, cleaning and disinfection of portable-toilet bottoms, and measures to limit renewed soiling into their daily work. Several commercial cleaning and disinfecting products were used according to location; this was not an experiment isolating the effect of one ingredient. No additional air purifiers were installed, nor were their operating hours extended.
After one year, local odor intensity at a urine-scaled portable toilet fell from 4.5 to 2.0, and at the urine-smelling carpet area from 4.0 to 1.5. β-Glucuronidase-active bacteria fell below detection limits at both locations, and the p-cresol indicator values also decreased.
The before-and-after p-cresol figures were relative values, with the outdoor concentration at each measurement time set to 1. They fell from 26 to 1 for the toilet and from 7 to 1.5 for the carpet. Because these values were normalized to outdoor concentrations, they do not mean that the total amount of odor fell by those same factors.
Ratings inside the facility decreased, but some odors remained
The staff surveys are reported as involving 52 people before the measures and 31 afterward. Another pre-intervention figure gives 54, so this account follows the methods section and Figure 9, which presents the before-and-after comparison. It could not be confirmed that individual staff responses were paired across the two surveys.
At the strongest-smelling location, just before the hospital-side access door, mean odor intensity decreased significantly from 3.0 to 2.0 (p=0.002). Ratings near the service station also decreased significantly (p=0.03). At the entrance, however, ratings moved from 1.4 to 0.9 without reaching the conventional 5% significance threshold (p=0.06). Improvement cannot be treated as equally certain at every location.
Some odor remained near the sources after intervention. The authors identified urine collection bags as one contributor and reported that subsequent additional measures had only limited lasting effects. Nevertheless, staff continued the work, and the authors stated that the low-odor environment was maintained. They also suggested that visualizing test results helped motivate continued efforts, but workload and motivation were not separately evaluated with dedicated measures.
This was a before-and-after comparison at one facility, without a control facility, combining cleaning, disinfection, and prevention of soiling. It therefore cannot separate the contribution of each measure. Its value lies in showing the potential of a source-identification and intervention process to reduce odors both locally and in the surrounding space.
Summary
At this facility, clues to strong urine odor were found in specific locations such as portable-toilet bottoms and carpet. Researchers narrowed down the sources by combining p-cresol concentrations and tests for bacteria with an enzyme activity involved in breaking down odor precursors with human smell assessments.
After a year of measures focused on those locations, local odor, active bacteria, and p-cresol indicator values decreased. Staff ratings at the strongest-smelling location also fell from 3.0 to 2.0. The study suggests that even when odor seems embedded throughout a space, looking for specific sources can be a starting point for improvement.
All five authors were affiliated with Kao or Kao Professional Services at the time of the study. No separate funding or conflict-of-interest statement was found in the original paper examined.
Reference
Ishida H, Tazoe Y, Mori I, Yamada T, Matsufusa H. Malodor-eliminating effect on indoor malodor of elderly nursing homes by focusing on urine-odor-emitting sources. Journal of Japan Association on Odor Environment. 2018;49(2):129–138. doi:10.2171/jao.49.129.
