Are professional cleaners at high risk of contracting the novel coronavirus?

They should not be.: Professional cleaners are trained pro's and know how to deal with what they get into. Pro's must have proper protective equipment. It means that people who are not trained professionals, but are just doing cleaning work... well, they need to train themselves on how to avoid the various hazards they might encounter in their work environment, such as viruses, bacteria, toxic fumes, lack of air, etc.

Not necessarily: Professional cleaners should already be knowledgeable about how to keep themselves safe and use of any required PPE>