At my agency we have postings all around the lobby to cancel your appointment if you have symptoms of flu or cold. We have had to turn clients away for being ill before - so if it's very obvious (you constantly sneezing, coughing, etc) I'd say stay home. A therapist getting ill means they have to cancel a day or days worth of clientele - and that once they caught the sickness they possibly passed it to additional clients and therapists.