I have made contributions to two books on opera while I have been poorly. Ripping reads, both of them.

https://www.amazon.co.uk/Business-Opera-Ashgate-Interdisciplinary-Studies/dp/1472429451

https://www.amazon.co.uk/Opera-Media-Age-Technology-Popular/dp/0786473290/ref=sr_1_1?s=books&ie=UTF8&qid=1474551862&sr=1-1&keywords=opera+in+the+media+age