( CNN ) -- Authorities conducting autopsies on a family of four found dead in in their home in eastern Missouri said preliminary autopsy results showed that the family may have died from carbon monoxide inhalation , police said Friday . The four -- a couple in their late 20s , their 4-year-old son and their 3-year-old daughter -- were found dead Thursday afternoon , said police in the city of St. Clair . Police had been summoned to the house after the man 's co-workers became concerned that he had not gone to work for several days , said police Chief Bill Hammack . Inside , officers found the four bodies but no indication of foul play , he said . Family members told police they had last been in contact with the family Tuesday , when he complained that he was feeling sick and nauseated , Hammack said . According the Center for Disease Control , each year , nearly 500 people die in the United States from carbon monoxide poisoning , and as many as 20,000 visit emergency rooms for exposure from poorly maintained heating systems and gas-powered generators . `` Dangers from poorly maintained heating systems are really going to be the number one cause of carbon monoxide poisonings in the United States , '' Dr. Paul Garbe said on a CDC online video . `` CDC recommends that all homes have carbon monoxide detectors , '' Garbe said . `` I think it 's a great investment . It 's particularly important that you have carbon monoxide detectors near where people sleep at night . The worst location for a carbon monoxide detector is in the box without a battery , '' he said .
Police find no indication of foul play . The man had told family he was feeling sick , police say . Police : Preliminary autopsy indicates they may have died of carbon monoxide inhalation . About 500 people a year die of carbon monoxide poisoning in the U.S .