San Francisco may be America's most expensive city to live in, but it's also quickly becoming one of the dirtiest in the world as well.

NBC Bay Area journalists recently conducted a survey of 153 blocks of downtown San Francisco and found trash on every street.

Trash bags and litter are one problem, but the report found that used needles and human feces are also common sights downtown - even near upscale hotels, government buildings and in playgrounds.

In total, the journalists found 100 drug needles and more than 300 piles of feces during their investigation.

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Journalists with NBC Bay Area recently conducted a survey of trash on the street in downtown San Francisco

In total, the journalists found 100 drug needles and more than 300 piles of feces during their investigation

If stuck by a used needle, one can be infected with diseases like HIV or Hepatitis. Fecal matter is also not just a smelly nuisance. As it dries, the germs become airborne and if inhaled, can prove deadly - especially for children.

Confronted with the findings of the report, infectious disease expert Dr. Lee Riley told the station that the streets of San Francisco are getting worse even than the slums of developing countries.

'The contamination is… much greater than communities in Brazil or Kenya or India,' the UC Berkeley professor said.

Experts say the issue stems from the city's homeless problem. Because the city doesn't have enough temporary beds for the homeless, they are left out on the streets

Riley pointed out that slums in the countries mentioned are used as long-term housing for poor people, many of whom make an attempt to keep at least their homes and surroundings livable.

But the homeless who live on the streets of downtown San Francisco are routinely being kicked from one encampment to the next, and therefore, don't feel a sense of obligation to clean up after themselves.

This results are 'extreme contamination,' Riley told the outlet.

City Supervisor Hillary Ronen said the issue goes back to the city's homeless problem.

She says that too much of the focus has been on finding the homeless permanent housing. If the city had more temporary beds in shelters, the homeless would be off the streets and not leaving behind such a mess.

One of the dirtiest areas of town is the Tenderloin district, seen above in 2015

She says the city currently has 2,000 temporary beds but needs about 1,000 more, which will cost about $25million.

'We need to find a source of revenue,' said Ronen. 'Whether that's putting something on the ballot to raise business taxes or taking a look at our general fund and re-allocating money towards that purpose and taking it away from something else in the city.'

What's bizarre is that the city is already spending more than that on cleaning the streets - a task that seems pointless since they never end up staying clean anyway.

Mohammed Nuru, the Director of the Public Works Department estimates that half his budget - $30million - goes to cleaning up feces and needles from the street.