Abstract and Introduction
Abstract
Using data from 12 US health departments, we estimated mean serial interval for monkeypox virus infection to be 8.5 (95% credible interval 7.3–9.9) days for symptom onset, based on 57 case pairs. Mean estimated incubation period was 5.6 (95% credible interval 4.3–7.8) days for symptom onset, based on 35 case pairs.
Introduction
Since May 6, 2022, mpox (formerly monkeypox) cases have been reported across the globe. According to the Centers for Disease Control and Prevention (CDC), 85,115 confirmed mpox cases and 182 deaths have occurred in 110 locations across historically endemic and nonendemic regions as of January 25, 2023.[1] Mpox symptoms usually start within 3 weeks of exposure to monkeypox virus (MPXV) and may include fever, headache, chills, swollen lymph nodes, and exhaustion.[2] A rash usually develops within 1–4 days after onset of symptoms. MPXV is transmitted through close contact with infectious rash, scabs, or body fluids; respiratory droplets during prolonged face-to-face contact; and fomites such as clothing, towels, or bedding.[1] Transmission in the current outbreak has occurred primarily through close physical contact associated with sexual activities among gay, bisexual, and other men who have sex with men. Transmission of MPXV is possible from the time of symptom onset until all scabs have fallen off and fully healed.[3]
The serial interval is defined as the time between symptom onset in a primary case-patient and symptom onset in the secondary case-patient and depends on the incubation period (the time from a person's infection to the onset of signs and symptoms),[4] epidemic phase, and population contact patterns. The serial interval is critical for estimating the effective reproduction number (Rt) and forecasting incidence, both of which are important for understanding the course of an outbreak and the effect of interventions (e.g., antiviral drugs and vaccines). In the current outbreak, many patients report multiple anonymous sex partners or attendance at large events, such as festivals, in the 3 weeks before symptom onset, which has complicated efforts to identify primary and secondary case pairs. By using preliminary data from 17 mpox case pairs in the United Kingdom, researchers estimated the mean serial interval to be 9.8 days with high uncertainty (95% credible interval [CrI] 5.9–21.4 days).[5] An investigation of 16 primary and secondary case pairs in Italy indicated the estimated mean generation time, or time between infection of primary and secondary cases, to be 12.5 (95% CrI 7.5–17.3) days.[6] In this report, we estimate the serial interval and incubation period for symptom onset and rash onset for MPXV infection in the United States.
Emerging Infectious Diseases. 2023;29(4):818-821. © 2023 Centers for Disease Control and Prevention (CDC)
