Mpox, a disease caused by the monkeypox virus, saw a significant increase in cases from mid-2022. The variant in the 2022 outbreak, named clade IIb, spread globally, primarily affecting men who have sex with men. In response, there has been a growing need for effective isolation strategies that balance public health and personal freedom.

Using individual patient data of clade IIb mpox cases, the dominant clade during the 2022 outbreak in Europe and America, a study led by researchers at Nagoya University in Japan has proposed a sophisticated modeling framework to enhance isolation protocols for mpox patients.

Their results show that the current standard practice to end isolation is effective, but implementing testing-based protocols can further reduce unnecessary isolation after the infectious period. Their findings, published in Nature Communications, may improve our response strategies and reduce patient isolation times.

“Our approach emphasizes the critical role of understanding individual variations in viral shedding dynamics to minimize both the risk of prematurely ending isolation and unnecessary prolonged isolation,” said Shingo Iwami. “Based on our results, the use of PCR testing may reduce the burden of isolation on mpox patients while preventing further transmission, especially when the number of mpox patients is increasing.”

The primary method to control the spread of mpox has been to isolate infected individuals. Current recommendations for the isolation of patients with mpox are symptom-based. The average duration of symptoms is about 3 weeks.

However, the infection period of mpox differs among patients. Some health officials are concerned that strategies based on symptoms or fixed time periods may not address this variability. Consequently, individuals being released into the community may still be infectious.

Iwami and his colleagues aimed to refine isolation strategies by developing a modeling framework to characterize when infected individuals cease to be infectious, thus optimizing isolation protocols. They built the models using viral load in lesion samples from previous studies of mpox.

They found that the duration of viral shedding among individuals ranged from 23 to 50 days. The researchers also found greater variation in the duration of viral shedding among mpox cases that spread in Europe and the United States in 2022.

Using these data, the group compared three isolation strategies: a symptom-based rule where isolation ends when symptoms disappear; a fixed-duration rule where isolation ends after a fixed period, typically three weeks; and a testing-based rule where isolation is based on a negative test result with varying numbers and intervals of tests.

Their results showed that the fixed-duration rule provided a balance between the risk and unnecessary isolation but was less flexible. However, the testing-based rule shortened this period, depending on the number of tests and intervals. They concluded that, while the fixed-duration rule was effective, the testing-based approach offered a more tailored solution that could better match the infectious period of individuals.

“The testing-based rule proved effective in minimizing the risk of ending isolation prematurely and reducing unnecessary isolation time,” Iwami said. “According to our analysis, 63% of individuals in the analyzed population could benefit from reduced isolation periods using the testing-based rule compared to symptom-based or fixed-duration rules.”

“To maintain the risk of ending isolation early at below 5%, PCR testing optimized by our simulations could reduce isolation periods by more than a week on average compared to the general isolation rule that is based on the disappearance of symptoms,” he said.

“Our simulations showed that if patients are tested at intervals of 2 to 5 days and have three to four consecutive negative results, we can safely end their isolation,” he continued. “This underscores the limitations of one-size-fits-all isolation policies.”

Implementing a testing-based rule requires careful planning and resources but could be more effective in managing isolation duration and reducing the burden on isolated individuals. Public health policies could incorporate these insights into designing more flexible and responsive isolation strategies.

Using detailed viral load data and sophisticated modeling, public health authorities can develop more effective isolation protocols that minimize both the risk of prematurely ending isolation and unnecessary extended isolation.

Iwami said, “Although our study was based on clade IIb data, if similar data become available for clade Ib, the variant circulating in the current growing epidemic in Africa, we believe the approach of this study would be a useful tool for planning the optimal duration of infection prevention and control.”