Eighteen mosquitoes within Durango city limits tested positive for carrying the West Nile virus over the past week, the San Juan Basin Health Department reported Tuesday.

Flannery O’Neil, deputy director of programs for the health department, said with alarming viruses such as West Nile and Zika garnering more public attention, the Colorado Department of Public Health and Environment has joined with local agencies to increase mosquito surveillance.

As a result, San Juan Basin Health and Animas Mosquito Control District have submitted 267 mosquitoes for testing this summer, and nearly 20 came back positive for West Nile.

“Since we’ve had more capacity to do testing, we’re not surprised to see more come back positive,” O’Neil said.

O’Neil said the capacity for the mosquito-borne disease has existed in Southwest Colorado for some time – over the past five years, there have been 10 human cases in Archuleta and La Plata counties.

No human cases have been reported this year, O’Neil said.

According to a statement about the findings, only 1 in 5 people who contract West Nile exhibit symptoms, which can include fever, headache, joint pains, vomiting, diarrhea and rash, among others.

In rare cases, individuals can develop a serious neurological infection.

San Juan Basin Health reminded residents to use mosquito repellent, keep skin covered at dusk and dawn, eliminate standing water and use window screens.

Information was not available Tuesday on the location where the West Nile-positive mosquitoes were found.