Hypothetical timeline of multidrug-resistant tuberculosis transmission in a school in Zhejiang, China, 2013–2017. The vertical dashed lines indicate the tuberculosis (TB) identified time of the index patient and the first secondary patient. The connection among cases was established through an epidemiological investigation. Neighbors with TB who are in close contact with the index patient are numbered N1 to N4. Secondary patients are numbered P1 to P3. Patients diagnosed with TB were colored black. Contacts with tuberculin skin test-positive results are colored gray.