Five health threats and epidemics after natural disasters

Mental Health Conditions

In the wake of Hurricane Katrina, New Orleanians experienced a lot of hardships. More than $100 billion worth of damage was done to homes and businesses, thousands were displaced, and an estimated 1,836 people died. While the immediate physical harm from the event was horrifying, the impact on mental health took longer to understand.

The immense stress and trauma experienced by survivors of a natural disaster can have long-term effects. Conditions like chronic stress, depression, and post-traumatic stress disorder can be challenging to treat in the wake of a disaster—if, indeed, they are even diagnosed at all—due to strains on the healthcare system and financial hardships. When these conditions go untreated, they can have a significant impact on health and well-being.

This is true not just for those who lived through the tragedy firsthand, but also for caregivers who assist in the recovery. Relief workers experience burnout, trauma, and other types of psychological distress at a higher rate than the general population.

Five health threats and epidemics after natural disasters

Vector-borne Diseases

Certain diseases aren’t spread from person to person, but instead spread through vectors, like mosquitoes. Meteorologic events, such as flooding, hurricanes and cyclones, can wash away certain vectors’ breeding sites—only to cause an explosion in the number of new ones a week or two later. This can lead to huge increases in the vector population and, subsequently, outbreaks of the diseases they carry. In the case of mosquitoes, that could mean upticks in diseases like malaria or dengue fever.

While many countries have ways of controlling mosquitoes through efforts like spraying pesticides, natural disasters can interrupt these services, leaving vectors to reproduce unchecked. This is true even in developed countries like the United States, where vector-borne diseases like West Nile can flare up after flooding or heavy rains.

Zika virus, in particular, is a concern following extreme weather events, as it has been linked to birth defects and other pregnancy-related issues. The same mosquitoes that carry dengue virus and West Nile can also transmit Zika, and these species have been found in much of the United States and throughout the globe.

While outbreaks of Zika virus have so far been rare in the United States, severe flooding—like what occurred in Houston following Hurricane Harvey in 2017—could make some areas particularly vulnerable to the virus spreading as mosquito populations increase and displaced people return to their homes from other areas.

Five health threats and epidemics after natural disasters

Communicable Diseases

People often cluster together in times of devastation. Families and neighbors consolidate into undamaged homes, and evacuees may gather by the thousands at shelters or supply distribution points. When a lot of people are crammed into a small space, pathogens like viruses and bacteria can be passed from one person to another very quickly.

This is especially true for acute respiratory illnesses like colds and the flu. While many respiratory diseases tend to be mild, they can sometimes lead to serious conditions like pneumonia, especially in older adults and those with compromised immune systems. These pathogens jump from person to person through respiratory droplets—spread by wiping a runny nose and touching a doorknob, or coughing while in a crowd. If another person breathes in the droplets or touches their face after coming in contact with a contaminated surface, they can become infected, too. The more people infected, the faster it spreads.

Emergency shelters can be particularly vulnerable to these kinds of outbreaks. These often-temporary facilities can be poorly ventilated and overcrowded. That, coupled with difficulties maintaining normal hygiene and frequent hand-washing, can lead to communicable diseases spreading quickly.

It’s important to note that—while gruesome and upsetting—dead bodies left as a result of a natural disaster carry very little risk of disease. Unless the deaths were due to a few particular infections like cholera or ebola, it’s unlikely they would be a source for an outbreak. Body recovery shouldn’t divert resources from life-saving missions and early survivor care. It is, however, important for the psychological and spiritual recovery of the survivors.

Five health threats and epidemics after natural disasters

Physical Injuries and Infection

Earthquakes, rising waters, and high winds can all cause immediate physical threats, but injuries can happen even before a natural disaster happens. In 2005, Hurricane Rita hadn’t even made landfall when dozens of people died during an evacuation of Houston and the Texas coast. Fleeing an emergency carries its own risks, and the sheer number of frightened people involved in a major city evacuation practically guarantees some number of incidents will occur on the road. For example, during Rita, 23 people were killed in a single bus fire. Overloaded roads present a further hazard when traffic inevitably slows or stops. Gridlock can leave evacuees vulnerable in their vehicles when the storm hits.

Similarly, building collapses or windswept debris don’t just cause injuries during a serious weather event. Even after an event is over, structures can become unstable and collapse hours, days, or even weeks later. This is particularly true in the case of earthquakes when aftershocks push structures past their breaking point and result in rescue workers being exposed to new hazards.

Wading through flood water can also lead to a host of injuries. Without being able to see where you’re walking or swimming, you could fall through an uncovered manhole, trip on uneven ground, or get cut by sharp objects underwater. There could also be dangerous creatures swimming unnoticed beside you. When flooding caused by Hurricane Harvey hit Houston in August 2017, residents reported seeing alligators, snakes, and even balls of floating fire ants in the floodwaters.

Even if an injury isn’t life-threatening at the time, it can be later if not properly cared for. But in the wake of a disastrous event, clean water and bandages to disinfect and dress a wound can be in short supply, and a resulting infection can turn deadly. Tetanus, in particular, is a major concern in the wake of disasters. The bacteria live in dirt and dust—both of which often get kicked up or swept into water supplies during a major event. If they make their way into an open wound, it can have fatal consequences.

Tetanus shots can help prevent this from happening, but when medical personnel and supplies are stretched thin, vaccines can take a backseat to more pressing concerns. That’s why it’s so important to stay up-to-date on your shots before a natural disaster looms.

Five health threats and epidemics after natural disasters


Haiti’s cholera outbreak was fueled by two key challenges often posed by disasters: unsafe water and lack of sanitation. The 2010 earthquake left many without access to clean water or bathrooms—including those working and staying at United Nations camps.

While it’s impossible to know for sure, a report by the United Nations suggests that a peacekeeper brought cholera with them to Haiti, and because of a lack of sanitation services, the bacteria made its way into a nearby river, contaminating the local water supply. At the time, Haitians downstream of the camp used the river water to drink, wash, bathe, and irrigate crops. As more and more people became infected, more bacteria got into the water supply, and within months, the country was facing a widespread epidemic.

In the wake of a disaster, thoroughly washing your hands or boiling your water can seem like almost an afterthought, but clean water is critical to keep death tolls from rising further. Diarrhea can lead to life-threatening dehydration, especially in young infants.

While Haiti’s outbreak was due to cholera, a lot of things can cause diarrhea. Flooded garages, machinery, or industrial sites can lead to toxins getting into floodwaters. Even in industrialized countries like the United States, you should take steps to prevent diarrhea: Wash your hands thoroughly after coming in contact with floodwaters and before eating, disinfect any flooded surfaces or objects—such as toys—before using them, and never swim or let kids play in flooded areas.

Five health threats and epidemics after natural disasters

Public Health Threats During and After a Natural Disaster

Less than a year after a devastating earthquake hit Haiti in 2010, public health officials on the ground noticed a curious phenomenon. Scores of people were getting sick with a disease that hadn’t been seen in Haiti in over a century: cholera.

The earthquake itself was catastrophic. More than 230,000 people were killed and 1.5 million displaced. The misery was then compounded by a cholera outbreak that would go on to sicken roughly 300,000 people and kill over 4,500. This was tragic—and preventable—but not necessarily unexpected.

While immediate casualty totals are what’s often cited following a natural disaster, the events can have long-lasting, detrimental effects on a population. When critical infrastructure is interrupted and people are displaced, it can make way for myriad public health problems, and understanding these problems is important for first responders and second-wave recovery efforts.

People on a flooded highway after natural disaster