Individuals or systems that provide the necessary conditions for pathogens to multiply rapidly and to become major sources of transmission of viruses or bacteria to the wider community.
Early reports of the COVID-19 pandemic suggested that the Wuhan Huanan seafood wet market in China was an amplifier for the spread of SARS-CoV-2 however, 13 of the first 41 cases had no link to the market.
Evolutionary biologists have analysed the viral genome of the early cases and suggest that the first few infections must have occurred in October 2019 outside the wet market and that perhaps, one of those people who were infected visited the market.
The other possibilities are that the virus jumped to humans from a single animal or a group of animals that were brought to the market. In zoonoses and vector-borne diseases, an amplifier host becomes a major source of infection for vectors, who carry the infection
Infectious Disease Transmission