Epidemiological, Clinical, And Public Health Response Characteristics Of A Large Outbreak Of Diphtheria Among The Rohingya Population In Cox'S Bazar, Bangladesh, 2017 To 2019: A Retrospective Study

BackgroundUnrest in Myanmar in August 2017 resulted in the movement of over 700,000 Rohingya refugees to overcrowded camps in Cox's Bazar, Bangladesh. A large outbreak of diphtheria subsequently began in this population.Methods and findingsData were collected during mass vaccination campaigns (MVCs), contact tracing activities, and from 9 Diphtheria Treatment Centers (DTCs) operated by national and international organizations. These data were used to describe the epidemiological and clinical features and the control measures to prevent transmission, during the first 2 years of the outbreak. Between November 10, 2017 and November 9, 2019, 7,064 cases were reported: 285 (4.0%) laboratory-confirmed, 3,610 (51.1%) probable, and 3,169 (44.9%) suspected cases. The crude attack rate was 51.5 cases per 10,000 person-years, and epidemic doubling time was 4.4 days (95% confidence interval [CI] 4.2-4.7) during the exponential growth phase. The median age was 10 years (range 0-85), and 3,126 (44.3%) were male. The typical symptoms were sore throat (93.5%), fever (86.0%), pseudomembrane (34.7%), and gross cervical lymphadenopathy (GCL; 30.6%). Diphtheria antitoxin (DAT) was administered to 1,062 (89.0%) out of 1,193 eligible patients, with adverse reactions following among 229 (21.6%). There were 45 deaths (case fatality ratio [CFR] 0.6%). Household contacts for 5,702 (80.7%) of 7,064 cases were successfully traced. A total of 41,452 contacts were identified, of whom 40,364 (97.4%) consented to begin chemoprophylaxis; adherence was 55.0% (N = 22,218) at 3-day follow-up. Unvaccinated household contacts were vaccinated with 3 doses (with 4-week interval), while a booster dose was administered if the primary vaccination schedule had been completed. The proportion of contacts vaccinated was 64.7% overall. Three MVC rounds were conducted, with administrative coverage varying between 88.5% and 110.4%. Pentavalent vaccine was administered to those aged 6 weeks to 6 years, while tetanus and diphtheria (Td) vaccine was administered to those aged 7 years and older. Lack of adequate diagnostic capacity to confirm cases was the main limitation, with a majority of cases unconfirmed and the proportion of true diphtheria cases unknown.ConclusionsTo our knowledge, this is the largest reported diphtheria outbreak in refugee settings. We observed that high population density, poor living conditions, and fast growth rate were associated with explosive expansion of the outbreak during the initial exponential growth phase. Three rounds of mass vaccinations targeting those aged 6 weeks to 14 years were associated with only modestly reduced transmission, and additional public health measures were necessary to end the outbreak. This outbreak has a long-lasting tail, with Rt oscillating at around 1 for an extended period. An adequate global DAT stockpile needs to be maintained. All populations must have access to health services and routine vaccination, and this access must be maintained during humanitarian crises.Author summaryWhy was this study done?Following the mass displacement of a highly vulnerable Rohingya population from Myanmar to Bangladesh in 2017, a large outbreak of diphtheria, a vaccine-preventable disease, occurred and spread rapidly, eventually lasting over 2 years. A large-scale international response effort was mounted to respond to the crisis, involving case isolation and treatment; tracing their close contacts and administering preventive antibiotic treatment; and mass vaccination campaigns (MVCs).Few, if any, previous studies have documented the epidemiological, clinical, and public health response characteristics of large outbreaks of diphtheria among vulnerable populations. We aim to provide such information to inform future public health response efforts.What did the researchers do and find?Between November 2017 and November 2019, 7,064 cases of diphtheria were identified. Most of the cases were among children, although a larger than expected proportion occurred among adults. Case fatality was low, with just 45 deaths.Symptoms were typical of diphtheria: sore throat (93.5%), fever (86.0%), pseudomembrane (34.7%), and gross cervical lymphadenopathy (GCL; 30.6%).Diphtheria antitoxin (DAT) was administered to 1,062 (89.0%) out of 1,193 eligible patients, with adverse reactions following among 221 (20.8%). A total of 41,452 household contacts were identified, of whom 40,364 (97.4%) consented to chemoprophylactic antibiotic therapy. An MVC achieved high coverage among the target population.What do these findings mean?High population density, poor living conditions, and fast growth rate caused explosive expansion of the outbreak during the initial exponential growth phase.Three rounds of mass vaccinations targeting children were associated with only modest reductions in transmission, and additional public health measures were necessary to end the outbreak.Diphtheria outbreaks in refugee settings may have a long-lasting tail and may require additional public health measures, such as expanded target age groups for vaccination, to bring to an end. Ensuring laboratory capacity for differential diagnosis in remote field sites is an important challenge.