of differentiating between causes of encephalitis and meningitis. Prevention Many of the guidelines for preventing occupational West Nile virus exposure are common to all mosquito-borne diseases. Public health measures include taking steps to reduce mosquito populations. Personal recommendations are to reduce the likelihood of being bitten. General measures to avoid bites include: Using insect repellent on exposed skin to repel mosquitoes. Repellents include products containing DEET and picaridin. DEET concentrations of 30% to 50% are effective for several hours. Picaridin, available at 7% and 15% concentrations, needs more frequent application. DEET formulations as high as 30% are recommended for children over two months of age. The CDC also recommends the use of: IR3535, oil of lemon eucalyptus, para-menthane-diol, or 2-undecanone. Protect infants less than two months of age by using a carrier draped with mosquito netting with an elastic edge for a tight fit. When using sunscreen, apply sunscreen first and then repellent. Repellent should be washed off at the end of the day before going to bed. Wear long-sleeve shirts, which should be tucked in, long trousers, socks, and hats to cover exposed skin (although most fabrics do not totally protect against bites). Insect repellents should be applied over top of protective clothing for greater protection. Do not apply insect repellents underneath clothing. Repellents containing permethrin (e.g., Permanone) or other insect repellents may be applied to clothing, shoes, tents, mosquito nets, and other gear. (Permethrin is not suitable for use directly on skin.) Most repellent is generally removed from clothing and gear by a single washing, but permethrin-treated clothing is effective for up to five washings. Most mosquitoes that transmit disease are most active at dawn and in the evening dusk. A notable exception is the Asian tiger mosquito, which is a daytime feeder and is more apt to be found in, or on the periphery of, shaded areas with heavy vegetation. They are now widespread in the United States, and in Florida they have been found in all 67 counties. In an at-risk area, staying in air-conditioned or well-screened room, or sleeping under an insecticide-treated bed net is recommended. Bed nets should be tucked under mattresses, and can be sprayed with a repellent if not already treated with an insecticide. Monitoring and control West Nile virus can be sampled from the environment by the pooling of trapped mosquitoes via ovitraps, carbon dioxide-baited light traps, and gravid traps, testing