London:Scientists have found evidence to show that the monkeypox virus can spread from an infected person up to four days before they even start exhibiting symptoms of the disease, a new study has claimed. The researchers behind the study estimated that 53 per cent of the transmission of monkeypox occurred in this pre-symptomatic phase, meaning that many infections cannot be prevented by asking individuals to isolate after they notice their symptoms.
According to them, if these findings published in the British Medical Journal are supported by other studies, pre-symptomatic transmission "would have important implications for infection control globally". While previous research on pox viruses did not rule out transmission prior to symptoms, this work represents the first evidence to support this. To explore this further, researchers at the United Kingdom Health Security Agency set out to analyse the transmission dynamics of the monkeypox outbreak in the country, the study said.
The two main measures of interest to the researchers were serial interval the time from symptom onset in the primary case patient to symptom onset in the secondary contact and incubation period the time from exposure to onset of symptoms. The mean incubation period was estimated to be 7.6 days in one model and 7.8 days in the other model, while the estimated mean serial interval was eight days in one model and 9.5 days in the other.
For both models, the median serial interval was between 0.3 and 1.7 days shorter than the median incubation period, indicating that considerable transmission is occurring before the appearance or detection of symptoms. Their findings are based on routine surveillance and contact-tracing data for 2,746 individuals who tested positive for the monkeypox virus in the UK between May 6 and August 1, 2022. Their average age was 38 years and 95 per cent of them reported being gay, bisexual, or men who have sex with men, the study mentioned.
To estimate the above values, the scientists linked information on exposure and symptom onset dates from these individuals to their contacts through contact-tracing case questionnaires, which they then analysed using two statistical models. The models were adjusted for several biases common to virus outbreaks, such as changes in infection rates over time, that would otherwise affect the results.
Analysis of individual-level patient data, collected from a subset of patients with more detailed information, seemed to confirm this explanation, with 10 out of 13 case-contact patient pairs reporting pre-symptomatic transmission. Four days was the maximum time that transmission was detected before symptoms appeared.