Since August 1, Madagascar health officials have reported 1,365 total cases of plague (confirmed, probable, and suspected) and 106 deaths, although case and death counts vary by news source. While Madagascar is no stranger to plague—it reports about 400 cases annually—this outbreak is larger and deadlier than previous outbreaks in the island nation.
In a previous Outbreak Thursday post, Outbreak Observatory examined the driving forces behind this outbreak’s rapid spread, including its entry into dense urban areas, such as the capital city of Antananarivo, and the high proportion of pneumonic plague among infected individuals. The highly transmissible pneumonic variant continues to be the predominant form of the disease, accounting for roughly two-thirds of the cases (915 pneumonic and 275 bubonic). Only one case of septicemic plague has been reported, and 174 cases remain unclassified.
Today we investigate two outstanding questions with respect to the size of the epidemic and effective response measures.
What is the actual case count?
One major challenge in determining the magnitude of the Madagascar plague outbreak is identifying confirmed cases. Despite elevated media coverage in recent days, many news outlets do not distinguish between the number of suspected, probable, and confirmed cases. While the severity of the situation should not be underestimated, a UNICEF situation report on October 22 revealed that only 10% of total cases have been confirmed by laboratory diagnostics (131 cases of approximately 1,300 total reported).
If past plague epidemics are any indication, many of these suspected cases are unlikely to be caused by Yersinia pestis. For instance, during a large reported plague outbreak in Surat, India in 1994, any individual in the outbreak area who presented with fever was classified as a suspected plague victim. More than 6,000 reported cases of plague in this outbreak were ultimately attributed to other diseases, and a team from the WHO was unable to conclusively culture Y. pestis from any suspected cases at the time. Regardless, WHO plague control guidelines state that all cases of plague—even suspected ones—should begin antibiotic treatment immediately due to the rapid onset of symptoms.
Will travel restrictions and traveler screening be effective in preventing spread to other countries?
A WHO external situation report from October 26 identified a low risk of global spread and moderate risk of regional spread, although nine countries and overseas territories are identified as “priority countries...for plague preparedness and readiness by virtue of having travel and trade links to Madagascar.” The countries and overseas territories listed include: Comoros, Ethiopia, Kenya, Mauritius, Mozambique, Reunion (France), Seychelles, South Africa, and Tanzania. The report emphasizes, however, that no epidemiologically linked cases have been reported outside of Madagascar, and the WHO advises against any travel or trade restrictions at this time.
Contravening the WHO guidelines, Seychelles implemented travel restrictions, with Air Seychelles temporarily suspending its service to Madagascar until further notice. This decision was made at the request of the Seychelles Public Health Authorities due to concern over importing plague from Madagascar. The Seychelles Ministry of Health reported around a dozen suspected cases of plague on October 10, but after extensive contact tracing and laboratory testing of samples collected from those suspected cases, the WHO reported last week that all individuals tested negative for Y. pestis.
Although Outbreak Observatory found no systematic analysis of the efficacy of travel restrictions in controlling plague, prior uses of these measures have led to huge economic losses and social tolls. For instance, trade and travel embargoes placed on India during the 1994 plague outbreak led to economic losses estimated at $1.7 billion. In previous outbreaks of other diseases, such as the 2009 H1N1 pandemic, the WHO warned countries against implementing non-evidence-based restrictions on trade or travel as a means of controlling the spread of disease. The Seychelles Ministry of Health informed the WHO that it intends to justify its public health rationale for violating the WHO guidelines and interfering with international travel. It will be interesting to see what data are provided to support these measures.
Meanwhile, several at-risk countries have implemented traveler screening protocols in response to the epidemic. In order to identify symptomatic travelers, Madagascar has implemented exit screening, which the WHO states will help mitigate the risk of international spread. Comoros, Mauritius, and South Africa have implemented entry screening for travelers arriving from Madagascar. Kenya has also increased surveillance of travelers entering the country from Madagascar, including requiring airlines that service Kenya from Madagascar to submit health declaration forms and sanitation certificates for aircraft passengers and crew at points of entry, according to Kenya’s Ministry of Health.
Ultimately, the “key readiness actions” for at-risk countries at this stage are public communication and education, enhancing surveillance efforts (including at points of entry), coordinating with health sector partners to develop response plans in advance of identifying cases, pre-positioning medical and response equipment and supplies, and providing international support such as technical assistance for epidemiological and clinical operations.
Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly in near-real time to allow others to learn from these experiences in order to improve global outbreak response capabilities.
Photo courtesy of National Institute of Allergy and Infectious Diseases (NIAID); Rocky Mountain Laboratories; NIH