Three weeks ago, Tropical Cyclone Idai made landfall on the coast of Mozambique in southern Africa. The storm, which peaked with winds in excess of 100 mph and a storm surge over 20 feet, led to massive flooding in Mozambique, Zimbabwe, and Malawi, taking more than 800 lives and displacing thousands of individuals. The damage caused by this storm has garnered international attention, and the response and recovery process will likely be extensive. Currently, there is an international effort to locate missing individuals and restore damaged systems in the affected nations.

Extreme weather events have the capability to fracture systems that deliver essential resources to affected populations. Damage to these key systems can create opportunities for outbreaks of otherwise preventable diseases. An excellent example of this is cholera, a waterborne disease that is commonly prevented through a functional water treatment system. Over the past 2 years, Outbreak Observatory has written about multiple instances of cholera around the world, where vulnerable health and water infrastructure has led to expansive outbreaks, including in Yemen (now more than 1.5 million cases) and Zimbabwe. Both of these are examples that highlight how cholera thrives in environments without adequate safe water delivery systems. Additional examples, such as the cholera outbreak that followed the 2010 earthquake in Haiti, illustrate that these types of risks can stem from a broad range of natural disaster events.

Tropical Cyclone Idai now joins this growing list after its winds and water assaulted the infrastructure and healthcare systems of countries in its path. Last week, representatives from the WHO spoke of the pressing challenges Mozambique faces in the wake of Tropical Cyclone Idai. Following the storm, thousands of individuals moved to temporary shelters after losing their homes, and the WHO shared that these individuals were at a “high risk” for cholera and other diseases that could see a surge in incidence following the storm. This at-risk population includes as many as 120,000 displaced individuals and others living without access to clean water. The remainder of this week’s Outbreak Thursday will look at how the WHO and other agencies are addressing this challenge, the reasons why Tropical Cyclone Idai caused so much damage, and the importance of increased public health preparedness in the face of future extreme weather events.

Responding to the Cholera Threat in Mozambique

During the relatively short timeframe following WHO’s announcement of a ‘high risk’ for cholera and other infectious diseases, Mozambique has reported 1,428 cases of cholera (as of April 2). The majority of these cases, and the only death, have been reported in Beira, a port city on Mozambique’s central coast with a population of approximately 500,000 people. The city was heavily impacted by Tropical Cyclone Idai, with flooding from rain and storm surge decimating its water system. The damage to Mozambique’s water delivery system became a primary public health concern providing waterborne diseases like cholera the opportunity to spread. Although Mozambique also experienced widespread flooding, damage to the system as a whole may present a more pressing concern than the floodwaters themselves. Floodwaters can contain infectious pathogens and serve as breeding grounds for certain vectors of disease, such as mosquitoes, but their impact on human health may be less immediate than contaminated systems that deliver water for drinking, food preparation, bathing, and other purposes.

The vast majority of cholera cases in the current outbreak have been reported in Beira (959 of the 1052 total cases through April 1), a trend that has continued as the outbreak has grown. To address the spread of this disease, the WHO selected Beira as the primary location for a 6-day mass vaccination campaign (commenced on April 3) that aims to outpace the spread of cholera in the 4 counties that Tropical Cyclone Idai hit most heavily. The WHO shipped 900,000 doses of oral cholera vaccines to Beira, and they are coordinating with relief organizations to expedite distribution and dispensing. There is heightened pressure to distribute these vaccines efficiently, with 11 emergency treatment centers constructed to address cholera in Beira alone. As of April 1, 9 of these centers were operational. Structural recovery of the city’s water system will have an extended timeline, so widespread dissemination of vaccines is critical for reducing the spread of this potentially lethal disease.

Why was this Storm so Bad, and What Does that Mean for Public Health Moving Forward?

Mozambique and its neighboring countries are no strangers to tropical cyclones. Mozambique averages approximately 1.5 tropical cyclones per year, but these storms are typically smaller than Idai. While tropical cyclones can cause significant damage, especially to coastal regions, Tropical Cyclone Idai was outside the range of expectations for a typical tropical cyclone, exhibiting a more severe storm surge and higher wind speeds than normally observed. Tropical Cyclone Idai’s severity was particularly surprising considering that the storm started its formation in the Mozambique channel, the strip of water between Mozambique and Madagascar. According to the National Geographic article cited above, storms that form in this area typically fail to grow to the size of Idai. Warmer atmospheric conditions associated with climate change do hold more moisture, which could have facilitated the increased rainfall observed during the storm.

Extreme weather events have the capability to decimate key components of infrastructure that play important roles in the health and wellbeing of populations residing in affected areas. The degree of damage is dependent on a myriad of factors, including the strength of the storm, the nature/status of infrastructure prior to the event, and local or national response capacity. Particularly severe extreme weather events, like Tropical Cyclone Idai, test the resilience of these systems, putting excessive stress on components of the system that can far exceed their operational capacity. Unfortunately, damage to key systems often requires an extended recovery process that can last months or even years and can divert limited financial resources from other programs, including future response efforts.

It has become widely accepted that changes to the Earth’s climate have a direct impact on the frequency and severity extreme weather events. The US Global Change Research Program’s National Climate Assessment directly addresses the increased incidence and severity of extreme weather as a potential outcome of a changing climate. From a public health perspective, the increased incidence of extreme storms, especially in areas with vulnerable health systems and infrastructure, presents challenges for safeguarding the health and wellbeing of global populations. Outbreak prevention and response rely on health systems to support their activities, and natural hazards like extreme weather events put these systems at risk. While global forces work to revise their strategies to better address severe weather events, the potential for disease outbreaks must be a key consideration for developing, implementing, and maintaining preparedness programs for these types of events.

Photo of Tropical Storm Irene courtesy of NASA Goddard MODIS Rapid Response Team

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.