Epidemiological characteristics of an urban plague epidemic in Madagascar, August–November, 2017: an outbreak report

Rindra Randremanana (1) , Voahangy Andrianaivoarimanana (2) , Birgit Nikolay (3) , Beza Ramasindrazana (2) , Juliette Paireau (3) , Quirine Astrid ten Bosch (3) , Jean Marius Rakotondramanga (1) , Soloandry Rahajandraibe (4) , Soanandrasana Rahelinirina (2) , Fanjasoa Rakotomanana (1) , Feno Jacob Rakotoarimanana (1) , Léa Bricette Randriamampionona (4) , Vaoary Razafimbia (4) , Mamy Jean de Dieu Randria (5) , Mihaja Raberahona (5) , Guillain Mikaty (6, 7) , Anne-Sophie Le Guern (8) , Lamina Arthur Rakotonjanabelo (9) , Charlotte Faty Ndiaye (9) , Voahangy Rasolofo (10) , Eric Bertherat (11) , Maherisoa Ratsitorahina (4) , Simon Cauchemez (3) , Laurence Baril (1) , André Spiegel (10) , Minoarisoa Rajerison (2)

1 IPM - Unité d'Epidémiologie [Antananarivo, Madagascar]
2 Unité Peste - Plague Unit [Antananarivo, Madagascar]
3 Modélisation mathématique des maladies infectieuses - Mathematical modelling of Infectious Diseases
4 Ministère de la Santé Publique - Ministry of Public Health [Antananarivo, Madagascar]
5 Hôpital Joseph Raseta Befelatanana
6 CIBU - Cellule d'Intervention Biologique d'Urgence - Laboratory for Urgent Response to Biological Threats
7 ERI - Environnement et Risques infectieux - Environment and Infectious Risks
8 Yersinia
9 OMS/WHO - Organisation Mondiale de la Santé - World Health Organization [Madagascar]
10 Institut Pasteur de Madagascar
11 OMS / WHO - Organisation Mondiale de la Santé / World Health Organization Office

Background: Madagascar accounts for 75% of global plague cases reported to WHO, with an annual incidence of 200-700 suspected cases (mainly bubonic plague). In 2017, a pneumonic plague epidemic of unusual size occurred. The extent of this epidemic provides a unique opportunity to better understand the epidemiology of pneumonic plagues, particularly in urban settings. Methods: Clinically suspected plague cases were notified to the Central Laboratory for Plague at Institut Pasteur de Madagascar (Antananarivo, Madagascar), where biological samples were tested. Based on cases recorded between Aug 1, and Nov 26, 2017, we assessed the epidemiological characteristics of this epidemic. Cases were classified as suspected, probable, or confirmed based on the results of three types of diagnostic tests (rapid diagnostic test, molecular methods, and culture) according to 2006 WHO recommendations. Findings: 2414 clinically suspected plague cases were reported, including 1878 (78%) pneumonic plague cases, 395 (16%) bubonic plague cases, one (<1%) septicaemic case, and 140 (6%) cases with unspecified clinical form. 386 (21%) of 1878 notified pneumonic plague cases were probable and 32 (2%) were confirmed. 73 (18%) of 395 notified bubonic plague cases were probable and 66 (17%) were confirmed. The case fatality ratio was higher among confirmed cases (eight [25%] of 32 cases) than probable (27 [8%] of 360 cases) or suspected pneumonic plague cases (74 [5%] of 1358 cases) and a similar trend was seen for bubonic plague cases (16 [24%] of 66 confirmed cases, four [6%] of 68 probable cases, and six [2%] of 243 suspected cases). 351 (84%) of 418 confirmed or probable pneumonic plague cases were concentrated in Antananarivo, the capital city, and Toamasina, the main seaport. All 50 isolated Yersinia pestis strains were susceptible to the tested antibiotics. Interpretation: This predominantly urban plague epidemic was characterised by a large number of notifications in two major urban areas and an unusually high proportion of pneumonic forms, with only 23% having one or more positive laboratory tests. Lessons about clinical and biological diagnosis, case definition, surveillance, and the logistical management of the response identified in this epidemic are crucial to improve the response to future plague outbreaks.

Domaines: Sciences du Vivant [q-bio]

Rindra Randremanana, Voahangy Andrianaivoarimanana, Birgit Nikolay, Beza Ramasindrazana, Juliette Paireau, et al.. Epidemiological characteristics of an urban plague epidemic in Madagascar, August–November, 2017: an outbreak report. The Lancet Infectious Diseases, 2019, 19 (5), pp.537-545. ⟨10.1016/S1473-3099(18)30730-8⟩. ⟨pasteur-02572610⟩