Anything out there fda approved to detect all human infectious diseases? how many test would be needed to achieve this request? 16srna and viruses?

Not to my knowledge: If you are having symptoms of what you think may be a viral illness it would be best to check with your pcp in order to run some basic test. CBC ESR etc. To my knowledge there is not an fda approved single test to detect any and all viral infections as there are many different viruses that are being detected, possibly related to destruction of their natural habitat (rain forest).