San Francisco declared a state of emergency - here's how the coronavirus is impacting the city, from a company's handshake ban to canceled conferences

Venture capital firm Andreessen Horowitz is taking precautions as the disease spreads, seemingly asking visitors to its San Francisco offices not to shake hands.

Technology researcher Tim Hwang posted on Twitter a photo taken outside the firm's offices, showing a sign that said: "Due to the Corona Virus, No Handshakes Please. Thank You."

The firm did not respond to Business Insider's request for comment, but Marc Andreessen posted a PSA on Twitter about the risks of hand-shaking as the virus spreads.

☣️💰☣️

no handshakes please

thank you pic.twitter.com/SOQ9ZqttB2

— Tim Hwang (@timhwang) February 6, 2020

☣️💰☣️

no handshakes please

thank you pic.twitter.com/SOQ9ZqttB2

— Tim Hwang (@timhwang) February 6, 2020

Facebook was planning to host its Global Marketing Summit in San Francisco from March 9 to 12, but recently canceled the event because of the coronavirus.

"Out of an abundance of caution, we canceled our Global Marketing Summit due to evolving public health risks related to coronavirus," Facebook spokesman Anthony Harrison said.

Verizon, AT&T, and IBM pulled out of the RSA Conference, one of the biggest cybersecurity conference events in the world. The companies are among 14 event sponsors to leave the event because of the coronavirus.

Another conference, the Game Developers Conference, also lost attendees over concerns about the virus. Facebook, Facebook's Oculus, and Sony won't be attending the event, which is scheduled to be held in San Francisco from March 16 to 20 at the same venue that Facebook's cancelled conference would have been held.

GDC said that the conference will include measures to prevent the spread of the virus on-site.

The economic impact of the cancellations are likely to be big. The Facebook event typically brings in about 5,000 guests, and San Francisco estimates that visitors to the city for conferences spend around $567 per day.

Riders of the Bay Area Rapid Transit (BART) system are raising their concerns about cleanliness on public transit as the virus spreads.

Residents told local outlet KRON4 that they and their families were fearful of riding on the trains and possibly contracting the virus from the crowds of people riding on them.

One rider told the news outlet that she thinks the transit authority could sanitize the trains, but speculated the cost could be high.

Mary Ann Richichi said, "I'm not really sure what they can do I mean unless they're gonna pay to have people go through the cars every night, try to sanitize them which would probably be a good idea but I don't know what cost that would be to the city but it would certainly be helpful."

Another rider said that the BART could provide hand sanitizer for riders getting on and off buses.

One rider said he doesn't touch anything on the trains and won't even sit down for fear of the germs.

"I don't touch anything on public transportation," rider Ed Sweeney told the outlet. "It's too dirty for me in the beginning. If we cleaned it up a little bit, maybe I would sit down."

Tech giants like Apple, Facebook, and Google, which have a heavy presence in San Francisco, are restricting employee travel as the virus spreads around the world.

Facebook, for example, said earlier this month it halted all non-essential employee travel to China, and was asking employees in China to work from home.

You can read a complete list of companies restricting travel here.

The virus is impacting tech companies' revenue forecasts, production plans, and retail stores.

Apple warned that its revenue would dip because of the coronavirus outbreak. It said store closures, as the company closed its stores in China and reopened some of them, could impact revenue.

It also said that production of iPhones in China would be slower because of the outbreak.

After the US said this week that Americans should prepare for a "significant" disruption to everyday life and a WHO official said that the world is "not ready" for an outbreak, markets around the world took a hit — including tech companies.