When a person is receiving chemotherapy, as I was 5 years ago, the immune system takes a big hit and drops so low for a week or so during each chemo period they have to be so careful not to catch anything at all or it will be hospital on an antibiotic drip. The advice given at the danger periods is to stay off work, never go near any form of public transport, stay away from public places including the school gates, get plenty of fresh air outdoors in quiet places, have plenty of fresh air in your home, anti bacterial handwash - not just for yourself but for everyone that lives with you or visits your house as soon as they enter, anti bacterial spray in the kitchen and bathroom, all door knobs etc. and anything else you can think of along those lines. All sensible advice.