Cost Comparison of Rodent Soiled Bedding Sentinel and Exhaust Air Dust Health-Monitoring Programs

Abstract

Rodent vivaria have traditionally used soiled bedding sentinel (SBS) health-monitoring programs to detect and exclude adventitious pathogens that could affect research results. Given the limitations of SBS, a likely reduction in animal usage, and a decrease in animal care staff labor, exhaust air dust (EAD) health monitoring has been evaluated by several groups for its efficacy in detecting pathogens when used as a complete replacement for traditional SBS health-monitoring programs. Compared with SBS, EAD has also been shown to provide increased sensitivity for the detection of multiple pathogens. After implementing EAD at our institution, we conducted an analysis to compare the annual costs of the 2 health-monitoring programs. The EAD program was found to be 26% less expensive than SBS. In addition to these cost savings, EAD decreased the amount of time spent by the staff on heath-monitoring activities. For veterinary technicians, this decrease in time was calculated as a savings of 150 h annually, almost 3 h each week. Finally, the EAD program replaced the use of live sentinel animals, decreasing the associated yearly usage from 1,676 animals to zero.

Rodent vivaria have traditionally used soiled bedding sentinel (SBS) health-monitoring programs to detect and exclude adventitious pathogens that could affect research results. Given the limitations of SBS, potential reduction in animal usage, and decrease in labor for animal care staff, exhaust air dust (EAD) health monitoring has been evaluated and is now recognized for its efficacy in detecting pathogens when used as a complete replacement of or an adjunct to traditional health-monitoring programs.^{1-5,7-9,11,12-17} Previously, exhaust air dust PCR testing was found to be effective at detecting mouse hepatitis virus,^1-3 mouse norovirus,^12,17 Sendai virus,³ astrovirus,⁹ lactate dehydrogenase virus,¹⁰ Helicobacter spp.,^1,11,12,15 Rodentibacter pneumotropicus and R. heylii (previously Pasteurella pneumotropica),^{1,11,12,14,16} pinworms,^1,8,13 fur mites,^1,7,9,13,16 and enteric protozoa.^1,11,16 Because our institution uses Allentown IVC racks, we implemented the Sentinel EAD health-monitoring program offered by this vendor. This program uses an adapter specifically designed for these IVC rack exhaust plenums; the adapter captures EAD on a collection medium (developed in partnership with Charles River Laboratories); the exposed collection medium is then submitted to the testing laboratory for PCR analysis. Compared with SBS programs, this EAD health-monitoring program has been shown to provide increased sensitivity for the detection of multiple pathogens.^11,12,16

The use of EAD health monitoring is in line with the 3R principles of animal research, because it replaces the use of live animals as sentinels.¹² In addition, a decrease in expenses is presumed with EAD monitoring programs, which eliminate the need to purchase and maintain animals, time during cage change to transfer soiled bedding, and time and expenses for performing the necessary diagnostic tests on sentinel animals. We compared the yearly costs of both SBS and EAD programs at our institution to test the hypothesis that EAD would provide a cost-savings advantage over SBS.

Materials and Methods

SBS animals and husbandry.

Female Swiss Webster Mice (age, 3 to 4 wk; Taconic Biosciences, Rensselaer, NY) were used as sentinel animals. These animals were negative for the pathogens described later. Each side of IVC 70-cage racks (Jag 75 Micro-VENT Environmental System IVC Racks, Allentown Caging, Allentown, NJ) housed one sentinel cage. Each cage contained 2 sentinel animals in solid-bottom polysulfone IVC (19.69 × 30.48 × 16.51 cm; Jag 75 Micro-Barrier IVC, Allentown Caging). Mice were housed on 1/4-in. corncob bedding (Teklad 7097, Envigo, Indianapolis, IN), provided reverse-osmosis–treated water through an automatic watering system (Avidity Science [previously Edstrom Industries], Waterford, WI), and fed an irradiated diet (Teklad 2918, Envigo). Mice were provided cotton squares (NES 3600, Ancare, Bellmore, NY) or specialty paper (Enviro-dri, Shepherd Specialty Papers, Watertown, TN) for enrichment. All cages, bedding, and enrichment items were autoclaved prior to use. Animal cages were changed every 14 d within a Class II Type A2 Biosafety Cabinet (NuAire, Plymouth, MN). Animal rooms were maintained on 12:12-h light:dark cycle with humidity ranging from 30% to 70% and temperatures ranging from 68 to 76 °F (20.0 to 24.4 °C), in compliance with the Guide for the Care and Use of Laboratory Animals.⁶ Animals were checked daily by the animal care staff to assure the animals were in good health and that appropriate food, water, and cage conditions were present. Each calendar quarter, one sentinel mouse was removed for terminal diagnostic use and replaced with a recently ordered mouse. Therefore, 4 mice per sentinel cage were used annually. The Animal Resources Center is part of the AAALAC-accredited animal care and use program at the University of Chicago. All animal work was approved by the University of Chicago's IACUC. The animals described in this study were housed in 3 mouse barrier facilities at the University of Chicago. The average total daily census of these vivaria was 21,000 cages.

SBS animal maintenance costs.

The total daily direct cost to maintain each cage daily was calculated by adding the following costs: 1) animal care staff labor; 2) supplies, including the costs of the feed, bedding, enrichment items, personal protective equipment, and cage wash detergents; 3) general facility maintenance; and 4) departmental administrative support.

SBS veterinary technician time.

The average total time spent by the veterinary technician on the SBS program was estimated by evaluating the amount of time each procedure took to complete. This estimate involved the time to perform ear punching for identification, necropsies, and sample collection (blood, fecal, fur swab, and oral swab). The cost was then calculated by using the average veterinary technician's yearly wage at our institution. Fringe benefits were included, because they represent actual institutional direct cost for the veterinary technician time spent on the program.

SBS diagnostic testing costs.

Diagnostic samples for SBS testing were sent quarterly to Charles River Research Animal Diagnostic Services (Wilmington, MA). Testing was performed by using a combination of PCR analysis and serology, as previously described.¹² Testing was performed for the following agents: mouse hepatitis virus, Sendai virus, pneumonia virus of mice, mouse parvovirus, minute virus of mice, Theiler murine encephalomyelitis virus, reovirus type 3, mouse rotavirus, ectromelia virus, lymphocytic choriomeningitis virus, mouse cytomegalovirus, mouse adenoviruses 1 and 2, hantavirus, Mycoplasma pulmonis, Salmonella spp., Citrobacter rodentium, Clostridium piliforme, Streptobacillus moniliformis, Filobacterium rodentium, Corynebacterium kutscheri, pinworms (Syphacia obvelata and Aspicularis tetraptera), fur mites (Myobia musculi, Myocoptes musculinus, and Radfordia affinis), and Giardia spp. Mouse norovirus, Rodentibacter pneumotropicus and R. heylii (previously Pasteurella pneumotropica), and Helicobacter spp. were endemic in the vivaria except for a few designated agent-free rooms; therefore, testing for these 3 agents only occurred in those specific rooms. Charles River Laboratories 2019 equivalent list prices were used to calculate the total diagnostic testing cost for SBS.

EAD collection media.

One Sentinel EAD collection medium (Allentown) was placed into the exhaust plenum of each rack that previously housed sentinel animals and was collected and replaced quarterly for PCR testing according to the manufacturer's instructions and as previously described.^11,12,16

EAD technician time.

The average time spent by the veterinary technician on the EAD program was estimated by evaluating the amount of time each procedure took to complete, including the time for collecting the exposed collection medium and placing a fresh one. The cost was then calculated by using the average veterinary technician's yearly wage at our institution. Fringe benefits were included, because they represent actual institutional direct cost for the veterinary technician time spent on the program.

EAD diagnostic testing costs.

The collection media were sent to Charles River Research Animal Diagnostic Services (Wilmington, MA) quarterly, and the same pathogens as listed above for SBS were tested by PCR assay. Charles River Laboratories 2019 equivalent list prices were used to calculate the total diagnostic testing cost for EAD.

Cost comparison of SBS with EAD health monitoring.

The individual costs associated with SBS were summed, and a total direct cost for the SBS program was calculated. The same procedure was used to obtain EAD direct costs. We then compared the total direct costs of the 2 health-monitoring programs.

Results

SBS animal costs.

The 3 mouse vivaria had a total of 231 single-sided and 94 double-sided racks, for a total of 419 sentinel cages. To maintain the cages, 1,676 animals were ordered annually. The purchase price for each animal was US $9, for a total of US $15,084 in animal costs (Table 1). We calculated shipping cost by multiplying the number of mice shipped (419) quarterly at US $57 per 25 mice, thus yielding US $3,876 in transportation cost (Table 1).

Table 1.

Comparison of the total annual costs of SBS and EAD health monitoring

	Annual cost (US$)
Type of cost	SBS	EAD
Animal ordering	15,084	not applicable
Animal shipping	3,876	not applicable
Animal maintenance	137,642	not applicable
Technician time	7,190	1,683
Diagnostic testing	449,629	450,938
Total annual cost	613,421	452,621

SBS animal maintenance costs.

The 419 cages used annually accounted for a total direct maintenance cost of US $137,642 (Table 1).

SBS veterinary technician time.

Quarterly, ear punching required 1 min per animal. Performing necropsies and collecting diagnostic samples involved 6 min per mouse. These durations included the time for cage manipulation within the barrier facility. These values were based on estimates from years of experience in performing these procedures, recognizing that the time commitment can vary based on many factors, including the ease in collecting blood, whether necropsy lesions are identified, etc. We did not complete a time-in-motion study because we no longer house sentinel animals. Therefore, the time for these procedures was estimated as 195.3 h annually, which is 9.4% of the total hours worked by the technician, assuming an 8-h workday during 52 wk per year. The annual cost for this component was calculated as US $7,190 based on the average veterinary technician yearly wage at our institution (Table 1).

SBS diagnostic testing costs.

The annual total cost for diagnostic testing of SBS by using PCR analysis and serology was US $449,629 (Table 1). The diagnostic laboratory provided all necessary diagnostic supplies and covered the shipping cost of the samples as part of the fee to their clients.

Total annual SBS costs.

The costs of ordering and shipping animals, veterinary technician time, and diagnostic testing were summed to calculate the total yearly expense of the SBS program, which was US $613,421 (Table 1).

EAD collection media.

Together, the 3 mouse vivaria had 231 single-sided and 94 double-sided racks, for a total of 325 Sentinel EAD collection media used each quarter. Collection media were provided by the diagnostic laboratory as part of their fee to clients.

EAD technician time.

Quarterly collection of the exposed collection media and replacement with fresh media required, on average, 2.1 min per rack. This figure was based on 3 time-and-motion studies for this procedure and involved 2 technicians and an average of 44 racks during each study. Therefore, these procedures took 45.5 h per year, which is 2.2% of the total hours worked by the technician. The annual cost was calculated as US $1,683 based on the average veterinary technician yearly wage at our institution (Table 1).

EAD diagnostic testing costs.

The annual total cost for EAD PCR diagnostic testing was US $450,938 (Table 1). As was their usual practice, the diagnostic laboratory fee included shipping the exposed collection media to their facility.

Total annual EAD costs.

The veterinary technician time and diagnostic testing costs were added to calculate the total yearly costs of the EAD program: US $452,621 (Table 1).

Cost comparison of SBS with EAD health monitoring.

Annually, the EAD program cost US $160,800 less than the SBS program, which is a 26% cost savings.

Discussion

The current study compared the yearly costs of SBS and EAD health-monitoring programs at our institution. The costs of SBS were calculated by totaling the sentinel animal ordering and shipping costs, the maintenance cost of the animals, percentage of the veterinary technician's yearly wage spent on the program, and diagnostic testing costs. The costs of EAD were calculated by totaling the percentage of the veterinary technician's yearly wage spent on the program and diagnostic testing costs. The hypothesis that EAD provided a cost-saving advantage over SBS was proven, because the annual cost of the EAD program was found to be US $160,800 (i.e., 26%) less than the SBS program. Statistical analysis was not performed in light of the large difference in cost and the fact that this study was intended to be used as a practical resource that highlights the financial considerations for animal care programs considering the change to EAD health monitoring.

The total annual diagnostic testing costs were similar for the 2 programs. The significant cost savings came from the animal ordering and maintenance expenses, which are not necessary in the EAD program. These cost savings depend on many factors, including the daily census and type of racks used in a facility. In programs with a low census, these cost savings might not be as great, because the costs of purchasing and maintaining sentinel cages would be lower. However, in larger programs, these cost savings could be greater than those we calculated here. In facilities that do not currently use IVC racks that are adaptable for EAD monitoring, the upfront costs to purchase these products could be substantial. In addition, institutional diagnostic laboratory discounts can further affect cost comparison; however, we used list prices in this study to avoid this discrepancy.

In addition to providing cost savings, EAD reduced the amount of staff time. For the veterinary technician, this savings amounted to 150 h per year, almost 3 h each per week. A presumed benefit to the animal care staff was that they could stop moving soiled bedding during cage change; however, the time savings for this component was not calculated. In addition, we were able to provide 419 more cage slots for investigator use and to charge per-diems for these cages. These considerable savings in cost, time, and space likely would be highly beneficial to any laboratory animal program.

Finally, the EAD program decreased yearly live sentinel animal usage from 1,676 mice to zero; this component is consistent with the 3R principles of animal research because using EAD monitoring replaced the use of live animals. Previous reports have speculated or approximated the reduction in animals used after switching to EAD monitoring;^3,9,11,12-17 however, the current study is the first to determine the actual annual reduction in the number of animals used when a SBS program is replaced by an EAD program.

EAD PCR analysis is at least as effective as SBS at detecting multiple rodent adventitious pathogens;^{1-5,7-9,11,12-17} however, the current study is the first to examine the detailed cost differences associated with these 2 types of health-monitoring programs. Overall, the current study showed a considerable cost savings with EAD; however, the equivalent or improved detection of multiple pathogens through EAD monitoring^{1-5,7-11,12-17} was the primary factor in our institution's decision to switch to EAD monitoring.

The costs of surveillance testing depend on the pathogens analyzed and the frequency of testing. For our study, the testing frequency was the same for the 2 programs, thus permitting a direct comparison. When institutions switch to EAD monitoring, they may continue with the same pathogen screening list and testing frequency. However, institutions should regularly evaluate this panel to ensure that they are testing for relevant pathogens and are not spending money on unnecessary testing. For example, usually there is no reason to test for agents that are not on the institutional exclusion list, but new pathogens arise regularly. FELASA's guidelines provide a pathogen list and recommendations regarding testing frequency, which are good starting points for most institutions.⁴

We did not include indirect costs, such as overhead rates, in this exercise for 2 reasons. First, because overhead rates are conventionally applied to direct labor hours, they affect the costs of both health-monitoring methods to the same degree and, therefore, provide no further differentiation. Second, overhead and other indirect costs, such as depreciation and amortization, may vary more widely between institutions than the direct costs we tallied and, consequently, may be less meaningful when comparing the overall cost of these 2 health-monitoring methods.

Additional costs that could not be calculated in the current study included the time spent attending to health concerns in sentinel mice, which periodically developed spontaneous illnesses. If a condition was considered to be minor, treatment was provided by veterinary technicians. However, if welfare issues or concern regarding an adventitious pathogen outbreak were present, veterinarians performed terminal blood collections and necropsies, and blood and tissues were submitted to the diagnostic laboratory. Additional animals might also be needed to replace affected SBS animal if health issues arose. This situation exposes a limitation of EAD monitoring, given the potentially increased chance of missing emerging pathogens due to the absence of necropsies and histopathology. Institutions that switch to EAD health monitoring should be vigilant regarding testing sick colony animals to ensure that new and emerging pathogens are not overlooked.

Overall, this study is the first to highlight the cost advantage of switching to EAD health monitoring. This benefit complements the greater sensitivity of pathogen detection^{1-5,7-9,11,12-17} and the replacement of live animals when switching to EAD.