Evacuees exit a rescue boat in the flood waters of Tropical Storm Harvey in Port Arthur, Texas, U.S. in a still image from video August 30, 2017. (REUTERS/Greg Savoy)

HOUSTON, Aug. 31 (Xinhua) -- Nearly 40 people died or are feared dead in flooding or circumstances connected to Tropical Storm Harvey in Texas, according to local officials.

Medical examiners are in the process of confirming which deaths are related to the historic flooding. Authorities are still searching for some of those believed to have perished during the flooding in the region. Local officials expect the grim discoveries of additional bodies once the floodwaters retreat and the streams, rivers and bayous go back into their banks.

The Harris County Institute of Forensic Sciences said Wednesday night it had confirmed 18 storm deaths, all but one of which were accidental drownings. They were investigating 10 additional deaths as potentially storm-related.

Among those deaths is a family of six reported missing after their van was swept away by floodwaters in east Houston near Greens Bayou on Sunday afternoon.

At least six people have died in Galveston County near the Gulf Coast as a result of Harvey-related flooding, officials said Tuesday, and one other death may be storm-related. The total includes three confirmed deaths -- two in Dickinson and one in League City.

Deaths were also reported in four counties in south east of Texas.

Flood waters not only destroy homes and highways, but also bring with chemicals, heavy metals, sewage, debris and mosquitoes to people's homes in what officials have warned that residents are facing long-term health threats.

In a press conference, officials reminded residents to remain clear of flood water which could have dangerous debris, down power lines and snakes. They also reminded residents to stay vigilant to remove standing water to reduce the threat of mosquito-born illnesses.

"Prevention, prevention, prevention is the key," Dr. Humair Shaw, Harris County public health executive director said in the conference. Harris County is where Houston locates.

Shaw said that as much of the county remained underwater, the threats hidden beneath those murky tides have led to several injuries.

"When you expose yourself to flood waters, you put yourself at risk," he said, adding "if you've been exposed to flood water, do whatever you can do to disinfect yourself," he said.

As water begins to recede in most of the flooded roads in Houston, Xinhua correspondent saw there are people playing with flood water on the streets, or even fishing in lakes and rivers where the water level has risen dramatically since Hurricane Harvey made a landfall on Aug. 25 in Gulf Coast area in Texas.

In particular, Shaw asked parents keep their children from playing flood water.

He also addressed the importance of homeowners and business owners cleaning their homes and buildings after they take in water.

Wildlife can post a health risk. Standing water left after the flood recedes will leave an ideal breading ground for mosquitoes which can spread Zika virus.

Water-borne and person-to-person infections can also early spread after a disaster. Overwhelmed sewer systems bring people into contact with disease-spreading bacteria. Stomach illnesses are common after floods, public health officials said.