Conference Material > Abstract
Eisenhauer C
Epicentre Scientific Day 2024. 23 May 2024
BACKGROUND
Outbreak alert systems can offset the severity of measles epidemics by minimising response delays. Existing systems, however, are often too sensitive to be practical when identifying areas for reactive interventions. To redress this challenge, we present a simple alternative system that combines a weekly and triweekly suspected case threshold. First evaluated in the DRC in 2022, here we extend the evaluation of this system to the context of Niger.
METHODS
A large number of threshold combinations were evaluated against indicators of cases captured by intervention and false alert risk. Combinations were evaluated against admin 2 level surveillance data from the DRC and Niger from 2015-2024. Performance was then compared to standard recommendations from the WHO and MSF.
RESULTS
The two example countries have distinct epidemic profiles, with the DRC exhibiting mas epidemics and Niger showing strong annual seasonality. In both settings, the proposed alternative alert system outperformed the existing WHO and MSF recommendation. The WHO recommendation, which is triggered by four suspected cases occuring within one month in a given locale (here, admin level 2), performs similarly to the proposed alternative when selecting the most sensitive of threshold combinations. The MSF recommendation, which is triggered by a raw increase in number of cases for three consecutive weeks, performed markedly worse, capturing 50% or less of cases. This poor performance is predominantly attributable to the high volatility of weekly measles surveillance data.
CONCLUSION
This analysis presents a simple evidence based alert system to improve measles outbreak response. It has been assessed in two countries, Niger and the DRC, and found to outperform standard recommendations. At present the system is available for use in both countries via their respective surveillance dashboards. Ongoing work is being conducted to evaluate the system in settings with additional epidemic profiles, including areas with low burden and areas with poor surveillance.
Outbreak alert systems can offset the severity of measles epidemics by minimising response delays. Existing systems, however, are often too sensitive to be practical when identifying areas for reactive interventions. To redress this challenge, we present a simple alternative system that combines a weekly and triweekly suspected case threshold. First evaluated in the DRC in 2022, here we extend the evaluation of this system to the context of Niger.
METHODS
A large number of threshold combinations were evaluated against indicators of cases captured by intervention and false alert risk. Combinations were evaluated against admin 2 level surveillance data from the DRC and Niger from 2015-2024. Performance was then compared to standard recommendations from the WHO and MSF.
RESULTS
The two example countries have distinct epidemic profiles, with the DRC exhibiting mas epidemics and Niger showing strong annual seasonality. In both settings, the proposed alternative alert system outperformed the existing WHO and MSF recommendation. The WHO recommendation, which is triggered by four suspected cases occuring within one month in a given locale (here, admin level 2), performs similarly to the proposed alternative when selecting the most sensitive of threshold combinations. The MSF recommendation, which is triggered by a raw increase in number of cases for three consecutive weeks, performed markedly worse, capturing 50% or less of cases. This poor performance is predominantly attributable to the high volatility of weekly measles surveillance data.
CONCLUSION
This analysis presents a simple evidence based alert system to improve measles outbreak response. It has been assessed in two countries, Niger and the DRC, and found to outperform standard recommendations. At present the system is available for use in both countries via their respective surveillance dashboards. Ongoing work is being conducted to evaluate the system in settings with additional epidemic profiles, including areas with low burden and areas with poor surveillance.
Conference Material > Video
Eisenhauer C, Nikolay B
Epicentre Scientific Day Paris 2022. 21 June 2022
Conference Material > Abstract
Eisenhauer C, Nikolay B
Epicentre Scientific Day Paris 2022. 7 June 2022
BACKGROUND
Measles remains a substantial infectious disease burden in the Democratic Republic of the Congo (DRC) and the country faces annual epidemics. While outbreak alert systems can offset the severity of these epidemics by minimising response delays, there is currently limited consensus on which system to use and how it should be implemented. Here we propose and evaluate a simple alert system composed of two thresholds : the weekly and triweekly number of suspected cases.
METHODS
A large number of potential threshold combinations were considered and several indicators were used to assess performance, including the risk of an alert being false and the proportion of outbreak cases that the system is expected to capture. Performance outcomes were evaluated using historical surveillance data from 2015 to 2020. The variability of performance over time was also assessed.
RESULTS
In total, 20 threshold combinations were considered, including 8 possible weekly thresholds and 7 possible triweekly thresholds. Among these, two combinations were selected as the most performant. The first and more sensitive system combined a weekly threshold of 10 cases with a triweekly threshold of 15 and the second combined 20 with 35. While the highly sensitive system captured 10% more cases (85% of all cases compared to 76%), it also experienced a 25% higher risk of false alert (68% compared to 43%). While absolute outcomes for both systems were somewhat variable over time, their relative performance remained consistent.
CONCLUSION
This analysis presents a simple and evidence based alert system to improve response times for measles outbreaks in DRC. By relying only on suspected cases and basic calculations, it can be implemented easily and is not subject to the delays associated with lab confirmation. Ongoing work is being done to evaluate whether the thresholds proposed here can be reapplied in other contexts.
KEY MESSAGE
Alert systems can offset the severity of measles outbreaks by reducing response delays. Here we propose and evaluate a deliberately simple possible system for DRC.
This abstract is not to be quoted for publication.
Measles remains a substantial infectious disease burden in the Democratic Republic of the Congo (DRC) and the country faces annual epidemics. While outbreak alert systems can offset the severity of these epidemics by minimising response delays, there is currently limited consensus on which system to use and how it should be implemented. Here we propose and evaluate a simple alert system composed of two thresholds : the weekly and triweekly number of suspected cases.
METHODS
A large number of potential threshold combinations were considered and several indicators were used to assess performance, including the risk of an alert being false and the proportion of outbreak cases that the system is expected to capture. Performance outcomes were evaluated using historical surveillance data from 2015 to 2020. The variability of performance over time was also assessed.
RESULTS
In total, 20 threshold combinations were considered, including 8 possible weekly thresholds and 7 possible triweekly thresholds. Among these, two combinations were selected as the most performant. The first and more sensitive system combined a weekly threshold of 10 cases with a triweekly threshold of 15 and the second combined 20 with 35. While the highly sensitive system captured 10% more cases (85% of all cases compared to 76%), it also experienced a 25% higher risk of false alert (68% compared to 43%). While absolute outcomes for both systems were somewhat variable over time, their relative performance remained consistent.
CONCLUSION
This analysis presents a simple and evidence based alert system to improve response times for measles outbreaks in DRC. By relying only on suspected cases and basic calculations, it can be implemented easily and is not subject to the delays associated with lab confirmation. Ongoing work is being done to evaluate whether the thresholds proposed here can be reapplied in other contexts.
KEY MESSAGE
Alert systems can offset the severity of measles outbreaks by reducing response delays. Here we propose and evaluate a deliberately simple possible system for DRC.
This abstract is not to be quoted for publication.