Massachusetts public-health officials on Wednesday elevated the risk level for West Nile virus to “high” in 10 communities after laboratory tests detected 168 infected mosquito samples since mid-June. The classification covers Acton, Bedford, Billerica, Boston, Brookline, Carlisle, Chelmsford, Dracut, Lowell and Newton. While no human infections have been recorded in the state this year, State Epidemiologist Catherine Brown said the findings have “accelerated rapidly,” marking what she called the peak period for mosquito-borne transmission. The Boston Public Health Commission urged residents—especially people over 50 and those with compromised immune systems—to use insect repellent, wear long sleeves and limit outdoor activity from dusk to dawn. Authorities also advised eliminating standing water and repairing window screens to reduce mosquito breeding and indoor exposure. In a separate alert, Chicago health officials reported three human West Nile cases, prompting similar calls for preventive measures across the city. Most infected individuals experience mild or no symptoms, but the virus can cause severe neurological illness in vulnerable populations.