Mpox Beyond Sexual Contact: How Often Did It Spread to Other Close Contacts in 2022?

During the 2022 mpox outbreak in the United States, 94 percent of patients reported catching it through sexual or other intimate contact. Much less was known about the other routes — respiratory droplets, contaminated items, ordinary skin contact. Two jurisdictions that could count those exposures give a first estimate: about 1.5 percent of nonsexual close contacts fell ill.

What was counted

In August–September 2022, CDC asked jurisdictions for data on nonsexual contacts of mpox patients from May 1 to July 31. Most had none to report or could not separate nonsexual contacts because of limits in contact tracing. Tennessee and the District of Columbia could. A nonsexual contact meant exposure to respiratory droplets, direct contact with contaminated items, or non-intimate skin-to-skin contact with a patient, with no sexual contact in the previous three weeks. A secondary case was a contact who developed symptoms within 21 days.

The one Tennessee contact who became ill had received post-exposure vaccination.

Where the exposures happened (D.C.)

How it compares

The 1.5 percent rate is consistent with what has been reported among nonsexual contacts in countries where mpox is endemic. A systematic review in Central Africa found secondary attack rates among unvaccinated household contacts of 0 to 11 percent, with a pooled estimate of 8 percent.

Caveats

The rate could be off in either direction. Fewer than half of D.C.'s contacts, and none of Tennessee's, were interviewed after 21 days, so cases may have been missed. On the other hand, symptomatic contacts were not tested, which could inflate the rate — and early in the outbreak, before post-exposure vaccine was widely available, patients may have named extra contacts to help them get vaccinated. The data do not separate children from adults, and much was self-reported or incomplete.

What to do

Sexual and intimate contact drove the 2022 outbreak, but some nonsexual spread did occur. Contacts should be monitored for signs and symptoms after a known exposure, and told how to prevent infection and what to do if symptoms appear.

Sources

Based on "Notes from the Field: Transmission of Mpox to Nonsexual Close Contacts — Two U.S. Jurisdictions, May 1–July 31, 2022," by Ebony S. Thomas and colleagues (CDC, District of Columbia Department of Public Health, Tennessee Department of Public Health), Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention; a work of the United States government in the public domain.