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Back pain in the absence of systemic infectious symptoms is most likely mechanical (traumatic, degenerative) and not contagious. The most common non-traumatic back pain issues I see in my practice are related to side effects from the modern cholesterol lowering drug class "Statins" which cause myositis (inflammation of the muscles).
The differential diagnostic spectrum of back pain is diverse. Fortunately, most causes are relatively benign and self-limited. It can, however, be a sign of serious or even life threatening disease on occasion. When in doubt, check it out. See your personal physician if symptoms persist.