MPHD recognizes that infected adult mosquitoes can transmit diseases of public health importance. The preferred mosquito control strategies of the Department involve the use of non-chemical mosquito control methods including public education, breeding site reduction and application of larvicides as previously described.

However, despite intensive efforts to eliminate breeding sites and apply larvicides, there may be times when a significant and increasing number of infectious adult mosquitoes are present in an area. If this situation is present, the risk to humans is high. Public communication about risk and avoidance of mosquito bites is essential, but at that stage adult mosquito control is the only way to reduce the number of infected adult mosquitoes. Thus, while it is considered a "last resort", using adulticide to quickly reduce the population of infected adult mosquitoes may be necessary on some occasions and is an accepted and recommended way to reduce risk of disease.

When predetermined action thresholds (discussed below) are met or exceeded, adulticide application may be implemented to reduce risks of WN virus transmission by decreasing the density of infected adult mosquitoes.

Metropolitan Code of Laws (MCL) ¤10.32.180 governs public communication and opt-out provisions for mosquito spraying activities. Provision D of the ordinance states: "The department of health shall be relieved from any of the foregoing requirements of this section if the director of health determines that a documented threat to public health exists."

The revised policy of MPHD shall be to spray for adult mosquitoes ONLY when a documented threat to public health exists. Adulticide application will be considered at the level of CDC risk category 3. In prior years, the threshold for spraying was in CDC risk category 2. Based on prior documented risk, the department expects thresholds for spraying to be a rarely if ever, met and for spraying to be a rare event.

Because MPHD will spray for adult mosquitoes ONLY when a documented threat to public health exists, MPHD is exempt from the application of MCL ¤ 10.32.180. However, MPHD will comply with the communication expectations of MCL ¤ 10.32.180 in response to requests from the community.

If spraying occurs, MPHD will utilize ultra low volume (ULV) application of insecticides from equipment mounted on trucks for adult mosquito abatement once predetermined action thresholds are met or exceeded. The department currently applies sumithrin/piperonyl butoxide (Anvil 2+2) to control adult mosquitoes. This compound is registered by the Environmental Protection Agency for use in residential and recreational areas.

All application of pesticides will be conducted in compliance with applicable federal and state regulations.

The department will broadcast spray an area from the street. In rare occurrences, spray may be conducted from alleys or trucks might enter larger properties when the size of the property calls for such action.

Indicators of WN virus activity will include identification of pools of mosquitoes positive for WN virus, positive birds or human cases. MPHD will not use a single positive mosquito pool, sporadic positive bird, or individual human case as a trigger for spraying but as an indication to intensify mosquito surveillance in an area and fill potential gaps in surveillance.

Finding two or more positive pools of mosquitoes in the same area, collected 2-14 days apart will be considered evidence of focal amplification and sustained viral activity. This will be the primary action threshold considered in making a determination to apply adulticides.

The action threshold for application of Anvil by MPHD corresponds to recommendations at risk category 3 by the Centers for Disease Control and Prevention's (CDC) for phased response to WN virus surveillance data (see chart below). Spraying for adult mosquito control will be considered when surveillance demonstrates evidence of amplification of WNV.

Once surveillance data indicate a public health threat, spray locations, boundaries, and frequency of adulticide application will be decided based on the spatial distribution and density of vectors shown by surveillance, infected birds, distribution of human cases, local ecological considerations, population at risk, and other relevant factors.

Public Notification

If a decision is made to spray, MPHD will fulfill the communication expectations described in the ordinance, but opt-out provisions are not appropriate when adulticide application is conducted to reduce a documented threat to public health.

Steps will be taken to inform the public through local television, radio, print media, MPHD's website, emails to individuals who have requested individual notification and phone calls to homes in the area to be sprayed. MPHD will keep a database of cell phone numbers for individuals who want to be notified when a spraying event is scheduled. We will attempt to notify the individuals of spraying events using an automated phone system.

Signs will be posted in areas to be sprayed indicating "Mosquito virus risk. Spray zone." and will include date and time of spraying and the phone number and web site where additional information can be obtained.

Emergency rooms, poison control center, and physicians and veterinarians who are on the listserv for Tennessee Health Alert Network or a similar listserv will be advised by health alert of the plans for ULV, the profile of the agents used and the anticipated levels of exposure.

Additional Public Relations Steps

For persons who choose to take steps to avoid exposure to the spray, several warning opportunities are in place. First, public communication outlined above will indicate the areas to be sprayed and the time of day when spraying is planned. Lead trucks will drive ahead of the spray trucks as an additional notification of spraying. Horns (before 8:00 PM), flashing lights, and noise from the spray equipment will also help to alert pedestrians. These measures should be sufficient to forewarn pedestrians who wish to reduce potential for exposure to pesticides by moving away from the path of the truck.

ULV application applies <3 ounces of formula (2% anvil) per acre of land. The dose of pesticides for individuals who are outdoors in the swath of the ULV pesticide is low. This situation is not regulated by EPA and would be below thresholds for significant documented public health concern.

Because of potential for public concern, reasonable efforts to avoid spraying groups of people will be taken. For example, spraying in public parks where large numbers of people have congregated will be delayed and the area will be sprayed at a later hour.

The effectiveness of spraying efforts will be monitored by counting the numbers of mosquitoes in traps before and after spray events and calculating changes in the density of infected mosquitoes.

We will also create a database to record complaints related to mosquito management.

Human Case Surveillance

The goals of human case surveillance are to assess local impacts of WN virus, monitor trends and identify geographic areas in need of targeted mosquito control interventions. A positive case by itself will not be used as an independent trigger for application of adulticides.

MPHD works with Tennessee State Department of Health to conduct follow-up of potential human cases of West Nile disease in Davidson County. The Tennessee State Department of Health also attempts to keep health care providers informed of the procedure for definitive diagnosis via laboratory testing of potential arboviral infections.

When a laboratory confirmation of a human case is made, MPHD staff will provide educational materials to residents in the area, and provide information on mosquito breeding sites reduction and ways of avoiding mosquito bites to residents of Davidson County through local media. We may also deploy ad hoc traps to the area to obtain information on WN virus activity.

For more information on mosquito management, contact the Health Department at 340-5668 or through the Department's web site (http://healthweb.nashville.gov).

CDC Risk Category LEVEL 3

Evidence of sustained WNV activity in mosquito population:
o Two or more positive mosquito pools, geographically clustered, detected on more than one day, within 2 weeks) OR o a horse or human case clustered in space and time with one or more positive mosquito pools)
Level of Public Health Threat=Moderate
Planned Interventions:
o Enhanced Public Notification
o Source reduction o Continue surveillance
o Enhance mosquito surveillance in areas with positives
o Larviciding
o Consider localized Adulticide application

4 Spring Summer or Fall measures indicating WNV epizootic activity at a level suggesting high risk of human infection
o sustained high mosquito infection rates
o horse or mammal cases indicating an outbreak OR o a human case and high percentage of positive mosquito pools High
o Above responses plus
o Apply Adulticide application in areas of highest risk 5 Spring Summer or Fall
o Multiple human cases AND
o Conditions for continued risk (multiple positive mosquito pools) Outbreak in Progress
o Above response plus intensified adult mosquito control