I recommend Melvyn Bragg's Radio 4 programme "In Our Time" which I heard yesterday. Lord Bragg assembled experts: Steve Jones, Professor of Genetics at University College London, Sir Roy Anderson, Professor of Infectious Disease Epidemiology at Imperial College London and Mark Pallen, Professor of Microbial Genomics at the University of Birmingham and led a fascinating and informative discussion on the origins, history and survival mechanisms of the microbes/bacteria/viruses, etc. that sometimes afflict us with infections. There is an iPlayer facility on the webpage to listen to the programme.
And if you would like to reduce your own risk of succumbing to respiratory diseases, I recommend Dr Briffa's recent article about Vitamin D.