A Planet of Viruses by Carl Zimmer was a huge disappointment. I had pre-ordered it from Amazon, so I wasn't able to preview it before purchase. If I had been, I probably wouldn't have purchased it, and I advise you to preview it as well.
The main thing you have to know about this book is that it was written with grant money that came from a Science Education Partnership Award from the NIH as part of the "World of Viruses project." In other words, this isn't a book for a science nerd, it is a book for someone with a Bio 101 level of knowledge about viruses, a book designed to educate the public.
The book is only 109 pages, but the acknowledgements start on page 95. Moreover, the writing is large, and there are a few blank pages as well as photos that are present for purely decorative purposes (not to illustrate concepts). I was able to read the book over a couple short connecting flights, in between inadvertent naps.
The content does not delve much into the research or biochemistry of viruses. It stays at the level of "viruses are sooooo small that..." and "viruses can doing wacky things to the human body like..." I think this may be the first science book I have ever read where I--a Classicist at heart and not a biologist--was actually already aware of everything in the book. I could have written this book myself. In fact, I have told the 'amazing story' of the true-life jack-a-lope (one of the chapters in this book) as part of a web project in Introductory Microbiology. The only thing that was news to me was the Balmis Expedition, but that's history not virology.
Is this a good book for health care workers to read? Hard to say, but probably yes. I say yes despite the book's limitations because in my experience most HCW are relatively ignorant of viruses compared with bacteria. Many cannot even identify correct symptoms of flu and are still fairly ignorant of the history and prognostic course of HIV/AIDS. Nurses I know seem to have as much knowledge of virology from the movie Outbreak as from science literature. A general heightening of awareness of viruses would probably be of use. But if you are enough of a science nerd that you have ever once dipped into a professional virology journal and understood what you are reading, you can definitely pass on this book.