This study corroborates our previous finding that effective cockroach control alone, which significantly decreases or eliminates cockroach populations, can result in significantly reduced cockroach allergen levels in settled dust samples. Unlike our previous interventions, which consisted of intensive pest control and resulted in large reductions in environmental cockroach allergen concentrations, two different approaches of pest control were used in this study, and the magnitude of the allergen reduction was dependent on the thoroughness and effectiveness of the cockroach eradication efforts. The Treatment 1 homes received a similar intervention to the crossed-over control homes in our previous study5
and the outcomes (cockroach reduction and allergen reduction) were similar as well. The Treatment 2 homes, serviced by commercial pest control companies, also experienced significant reductions in the number of cockroaches trapped, but the magnitude of the reduction was significantly lower than in Treatment 1 homes, the cockroach infestation remained relatively high after 12 months, and changes in cockroach allergens were not different from those in untreated control homes.
What are possible reasons for the differences in the two treatment arms? We believe the major differences were related to cockroach monitoring which guided bait placement in Treatment 1 homes, the types of pesticides used, and the schedule and intensity of treatment. In the Treatment 1 arm, the cockroach populations were monitored throughout the study with 18 sticky traps per home, and homes were treated again if any cockroaches were trapped at months 1, 3, 6, and 9. Treatment 1 also used layout maps of each home, identified problem areas, and targeted aggregations of cockroaches extensively throughout the entire home at baseline and as needed throughout the 12 months of follow-up. Living rooms and bedrooms in these homes harbored significant infestations () that would likely reinfest other rooms if not eliminated. Treatment 1 utilized highly effective, reduced toxicity gel baits for every treatment, and did not use any spray or dust formulations. Thus, Treatment 1 closely approximated the fundamentals of integrated pest management, but with one major exception: preventing infestations (sealing cracks and crevices, caulking, and structural repairs), which is very labor intensive and expensive, was beyond the scope of this intervention study. The reduction of cockroaches by monitoring-guided insecticide baiting has been previously shown to be similar to that in an integrated program which included cleaning, resident education and baiting.11
Moreover, the monitoring-guided approach has been shown to be significantly more effective at reducing cockroach populations than baseboard and crack and crevice spray treatments.12
In contrast, the commercial pest control companies in Treatment 2 used predominantly “traditional” or “conventional” treatments, which generally consist of calendar-based (monthly, bimonthly, or quarterly) applications of spray and dust insecticide formulations to baseboards and cracks and crevices.12, 13
None of the contracted pest control companies used traps to monitor the cockroach infestation. The pest control companies usually treated only the kitchen and bathrooms, unless specifically requested by the residents to treat other areas. The majority of their initial treatments relied heavily on spray and dust formulations and utilized smaller amounts of gel baits. Spray insecticide label directions require that the contents of kitchen cabinets be removed or covered to prevent contamination; such preparations are generally left to residents and non-compliance may result in less thorough insecticide coverage. The majority of residents in Treatment 2 complained about the dusts, sprays and work involved in cleaning out cabinets, drawers, etc in their homes. These complaints were relayed to the companies, and according to resident reports and study staff observations, the types of insecticides used in Treatment 2 homes changed over time to include more bait stations and gel baits. Although we had 2 local, 1 regional and 1 national commercial company involved in this study, Treatment 2 results may not be typical of all commercial companies. The homes in this study were all cockroach infested row homes and low-rise apartments with adjacent units not involved in the intervention. These homes are similar to those found in other urban areas11, 12, 14-16
, although they may not be representative of cockroach infested homes in high-rise apartment buildings.
Despite significant reductions in cockroaches in Treatment 2 homes (e.g., 83% in the kitchen), allergen levels changed only marginally (e.g., 35.7% in the kitchen). This suggests the possibility that there is a threshold level of cockroach infestation, above which drastic decreases in cockroach allergen, like those seen in the Treatment 1, are unlikely. This threshold may represent a level of active cockroaches that disseminate allergen in feces and other secretions during normal foraging activities. The Treatment 1 homes received additional bait placement after any trapping visit in which more than 1 cockroach was trapped. In other words, the goal of Treatment 1 was eradication of cockroaches, not merely population control or management. Although this is likely also the goal of the commercial pest control companies that treated homes in this study, they had no means of assessing their effectiveness without monitoring the pest population.
The total cost of Treatment 1 was estimated at $281 per home for 12 months of follow-up including cockroach trapping, counting, and bait placement. The cost of the bait placement ranged from approximately $61 to $124 with a median cost of $80 for 12 months of treatment. The cost over 12 months for the cockroach traps, labor to place and retrieve the traps and labor to count the traps was $201 per home. The median cost for a 12-month contract with the commercial pest control companies in Treatment 2 was $475.
One limitation of this study is the lack of health outcome data to correlate with the reductions in cockroaches and cockroach allergen. This study did not undertake health outcome measures because we felt it was necessary to confirm our intervention methods were effective before enrolling asthmatic children or adults into a clinical trial. We are currently planning a multi-center clinical trial with moderate to severe asthmatic children who are both sensitized and exposed to cockroach allergen. The intervention from Treatment 1 will be implemented in their homes and health outcomes will be monitored. Based on data from ICAS showing a significant correlation between Bla g 1 reductions (44% reduction from a baseline median of 0.2 U/g dust) and decreased asthma morbidity3
, we anticipate that by reducing cockroach numbers and allergen to the degree demonstrated in the current study, a significant improvement in asthma morbidity will be achieved.
In this study, commercial pest control companies were not as successful at removing cockroaches and their allergens from homes in inner-city multi-unit dwellings as a group of entomologists; however, these companies did demonstrate effectiveness in reducing cockroach counts when compared to control and allergen concentrations within homes. To improve their effectiveness we would suggest additional training for pest control operators to increase their knowledge about the most effective treatments and education of patients to be diligent in reporting cockroach sightings to the companies and requesting additional service visits.
By monitoring cockroach trap counts and intensively treating infested homes with highly-effective gel bait preparations, cockroach populations can be dramatically reduced almost to the point of eradication. This reduction in cockroach infestation leads to a large reduction in cockroach allergen as well. The magnitude of the allergen reduction is dependent upon the success of the cockroach eradication efforts.