| 11. | The main source of infection is the country's network of desperately overcrowded prisons.
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| 12. | He said health authorities were continuing an investigation to pinpoint the source of infection.
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| 13. | DNA sequencing confirmed the source of infection in one instance.
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| 14. | Ears can be a source of infection for many animals.
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| 15. | Epidemiological fieldwork suggested fresh vegetables were the source of infection.
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| 16. | Contaminated feed is considered the most likely source of infection.
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| 17. | They are the sources of infection and they spread the disease to young people.
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| 18. | The discovery is significant because it may help investigators trace the source of infection.
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| 19. | "No evidence could be found of any other source of infection, " the statement said.
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| 20. | Contaminated food and drinks are the source of infection and how this toxin is spread.
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