Are there any common viruses or bacteria that would be viable after 3 years?

Hi,

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It would have been better if your query had been clear about whether you meant the normal circumstances inside the human body or in the environmental condition.

Inside the human body, bacteria and viruses can survive for many years without causing any clinical disease in the host and such type of hosts are called as carriers. When favorable conditions develop, these microorganisms leads to development of clinical diseases.

Second about environmental condition, viruses multiply only inside living host and they cannot survive outside their host for such a long period of 3 years. The duration for inactivation of viruses in the environment is different for different viruses. About bacteria, many bacterial species can survive in the environment for a long period if they have favourable environment. It includes many non-pathogenic and some pathogenic bacteria and also some opportunistic bacteria.