The transmission dynamics of the monkeypox outbreak in the United Kingdom

The transmission dynamics of the monkeypox outbreak in the United Kingdom

In a recently published study in BMJ, researchers analyzed the transmission dynamics of the monkeypox (MPX) virus (MPXV) among residents of the United Kingdom (UK).

Lernen: Übertragungsdynamik von Affenpocken im Vereinigten Königreich: Kontaktverfolgungsstudie. Bildnachweis: Dotted Yeti/Shutterstock

background

The ongoing MPX outbreak in 2022 has affected several nations, such as the United Kingdom, that are not endemic for the virus, and infected people with no recent travel history to endemic regions such as Central and West Africa. In July 2022, MPX was declared a global public health emergency by the World Health Organization (WHO).

About studying

In the present study, researchers analyzed MPXV transmission dynamics in the United Kingdom.

Data from case-contact pairs (CC) and potential exposure dates (EDs) linked through contact tracing and UKHSA (UK Health Security Agency) case questionnaires were analyzed. The symptom onset dates (SODs) for the CC pairs were identified based on matching the PINs (pseudo identification numbers) with the LLs (line lists), and 2,746 polymerase chain reaction (PCR)-confirmed MPX patients were included in the study between May 6 and August 1, 2022.

The primary study outcome was to determine the SI (serial interval) and IP (incubation period) of MPX using the interval censoring corrected (ICC) and IC right truncation corrected (ICRTC) time distribution models. Generalized additive modeling was used to assess the growth of MPX cases up to the reporting dates (date of reporting confirmed cases to the UKHSA).

For each CC pair, an individual with primary MPX infection was designated as the primary case (PC) and the individual infected by the PC was designated as the secondary contact (SC). Thus, CC pairs included individuals identified as contacts by cases who later became cases or were already cases. The last date of PC contact reported by an individual within three weeks before SOD was considered ED, and the date on which symptoms manifested was considered SOD.

To examine probable EDs that occurred before SODs in PCs, indicating MPXV transmission before symptom onset, PC-SOD data were linked to SC-EDs. CC pairs were linked to the questionnaire records for each SC, allowing identification of PCs and EDs for the SCs. PINs were then used to connect PCs to the LL to obtain the SODs.

Results

Omics eBook

Compilation of the top interviews, articles and news from the last year. Download a free copy

The average age of the study participants was 38 years, and most (95%) of them were reported as bisexual, gay, and other MSM (men who have sex with men). As of August 1, 2022, 92 records (from 650 questionnaires) with complete ED and PIN data required for data linkage have been obtained. Of these, documented CC links were available for 30 data sets, enabling PC identification.

Of the 30 PCs, SODs were documented for 19 PCs in the LL. A total of 220 CC pairs were reported, of which 79 had SODs for both individuals of the CC pair, forming the SI cohort. Of 650 people who completed the questionnaires, 54 provided SOD data and the date of last contact with a PC, forming the IP cohort.

Of 19 PC datasets, negative IP was reported in three datasets, which were therefore excluded from the analysis. Of the remaining PC records, seven PCs provided PII (personally identifiable information) in the LL and questionnaire, enabling PC verification. Four (of seven) cases had concordant PII, and after excluding the three discordant pairs, 13 CC pairs remained, forming the study cohort of presymptomatic MPXV transmission.

The average IP was estimated to be eight days using both time lag models, and the average SI was estimated to be eight days and ten days using the ICC and ICRTC models, respectively. Although the average SI lasted longer than the IP, short SIs were observed more frequently than short IPs, with the median and 25th percentile values ​​of the SI estimated to be shorter than those of the IP.

The modeled median and 25th percentile values ​​of ICRTC and ICC time distribution were one to two days and two days shorter, respectively. Of the 13 linked MPX patients, ten had reported presymptomatic MPX transmission. The time for MPX cases to double reduced from nine days on May 6, 2022, when MPXV was first detected in UK residents, to a halving time of 29 days on August 1, 2022.

Diploma

In summary, based on the study results, the peak of the MPX outbreak was observed in the United Kingdom on July 9, 2022, after which cases declined. Short SIs were observed more frequently than short IPs, suggesting significant presymptomatic transmission of MPXV, validated by linked patient health records.

In MPXV-infected and PII-associated patients, the maximum duration for which MPXV transmission was identified before SO was 4.0 days. Individuals would need to be isolated for a period of 16 to 23 days to identify 95% of those with probable MPX. For SI, the 95th percentile was found to be between days 23 and 41, indicating long periods of MPXV infections.

Reference:

• Ward, T. et al. (2022) „Übertragungsdynamik von Affenpocken im Vereinigten Königreich: Kontaktverfolgungsstudie“, BMJ, p. e073153. doi: 10.1136/bmj-2022-073153. https://www.bmj.com/content/379/bmj-2022-073153

.