Nowcasting the 2022 mpox outbreak in England

Abstract

In May 2022, a cluster of mpox cases were detected in the UK that could not be traced to recent travel history from an endemic region. Over the coming months, the outbreak grew, with over 3000 total cases reported in the UK, and similar outbreaks occurring worldwide. These outbreaks appeared linked to sexual contact networks between gay, bisexual and other men who have sex with men. Following the COVID-19 pandemic, local health systems were strained, and therefore effective surveillance for mpox was essential for managing public health policy. However, the mpox outbreak in the UK was characterised by substantial delays in the reporting of the symptom onset date and specimen collection date for confirmed positive cases. These delays led to substantial backfilling in the epidemic curve, making it challenging to interpret the epidemic trajectory in real-time. Many nowcasting models exist to tackle this challenge in epidemiological data, but these lacked sufficient flexibility. We have developed a nowcasting model using generalised additive models that makes novel use of individual-level patient data to correct the mpox epidemic curve in England. The aim of this model is to correct for backfilling in the epidemic curve and provide real-time characteristics of the state of the epidemic, including the real-time growth rate. This model benefited from close collaboration with individuals involved in collecting and processing the data, enabling temporal changes in the reporting structure to be built into the model, which improved the robustness of the nowcasts generated. The resulting model accurately captured the true shape of the epidemic curve in real time.

Evaluating the forecasting performance of ensemble sub-epidemic frameworks and other time series models for the 2022–2023 mpox epidemic

“…[7,[21][22][23][24][25][26] and mean absolute percentage error [21,[23][24][25]. Only two studies used probabilistic measures of performance, such as the weighted interval score (WIS) [7,29]. Of the studies included here, four focused on the ascending phase of the epidemic (January-mid-August 2022) [20,[24][25][26], three included forecasts of the epidemic's ascension and peak (February-September 2022) [21,22,29] and four focused on the ascending, peak and declining phases of the epidemic (January 2022-present) [7,23,27,28].…”

Retrospective evaluation of short-term forecast performance of ensemble sub-epidemic frameworks and other time-series models: The 2022-2023 mpox outbreak across multiple geographical scales, July 14th, 2022, through February 26th, 2023

“…Several methodologies have been employed to forecast the case trajectory of the 2022-2023 mpox epidemic in various geographical regions, including, but not limited to, models focused on human judgment [29], deep learning, and artificial intelligence models (AI) [30][31][32], machine learning models [30][31][32][33][34][35], statistical models such as auto-regressive integrated moving average (ARIMA) models [31,[33][34][35][36][37], compartmental models [38], and semi-mechanistic sub-epidemic models [16]. Performance metrics employed have mainly included variations of mean absolute error (MAE) [16,30,31,[33][34][35]37], mean squared error (MSE) [16,[30][31][32][33][34][35][36][37], and mean absolute percentage error (MAPE) [16,31,[33][34][35], with only two studies also including probabilistic measures of performance such as the weighted interval score (WIS) [16,39]. Of the studies included here, four focused on the ascending phase of the epidemic (January 2022-Mid August 2022) [29,…”

“…Performance metrics employed have mainly included variations of mean absolute error (MAE) [16,30,31,[33][34][35]37], mean squared error (MSE) [16,[30][31][32][33][34][35][36][37], and mean absolute percentage error (MAPE) [16,31,[33][34][35], with only two studies also including probabilistic measures of performance such as the weighted interval score (WIS) [16,39]. Of the studies included here, four focused on the ascending phase of the epidemic (January 2022-Mid August 2022) [29,33,34,36], four evaluated forecasts of the ascending and peak of the epidemic (February 2022-September 2022) [30][31][32]39], and four focused on the ascending, peak and decline phases of the epidemic (January 2022-Present) [16,35,37,38].…”