By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

Dr. Deresinski reports no financial relationships relevant to this field of study.

Among the dangers faced after a severe weather event is an increased risk of various infections.1 After Hurricane Katrina, the main types of infections seen were gastrointestinal, wound, respiratory, and skin.2 CDC has listed a panoply of post-disaster infections. (See Table 1.)

Waterborne infections resulting from exposure to flood waters or contamination of water supplies are of major concern. A systematic literature review of global waterborne outbreaks involving water-related weather events identified 93 reports dealing with 87 individual outbreaks in 29 countries.3 The most frequent causes were Vibrio spp. (most in Asia) and Leptospira spp. (most in North America and Asia). The water supply was confirmed as the apparent source of infection in 54.8% of instances in which testing was performed. The weather events consisted of heavy rainfall and flooding, each often resulting from hurricanes, in just over one-half. Contact with water most commonly occurred while wading or performing cleaning activities.

Among the identified problems were overwhelmed water treatment facilities and sewage systems. Among the cases in which the type of contaminated water source was stated, the main water supply was implicated in two-thirds and well water in one-third. The former source often was associated with outbreaks due to Campylobacter and Cryptosporidium. Pathogens associated with environmental water exposure, rather than water supply contamination, were Leptospira spp., Cryptosporidium spp., norovirus, and Vibrio vulnificus.

After Katrina the notable causes of diarrhea/gastroenteritis were norovirus, non-toxigenic Vibrio cholerae, and non-typhoidal Salmonella. An outbreak of norovirus is believed to have affected at least 1,000 individuals in a large evacuation center in Houston.4 Vibrio infections acquired in the United States almost always are caused by species such as Vibrio parahaemolyticus, V. vulnificus, and non-O1, non-O139 V. cholerae that are noncholeragenic, and no cholera epidemic was identified after Katrina. However, two cases of infection with toxigenic V. cholerae that appeared to be the result of eating undercooked or contaminated shrimp occurred in a Louisiana couple after Hurricane Rita (which occurred approximately one month after Katrina).5

Leptospirosis, not a cause of diarrhea, often results from exposure to environmental water and may be an important cause of febrile illness after flooding. As an example, after Hurricane Hortense in Puerto Rico, 17 of 70 (24%) febrile patients with a negative serological screen for dengue virus infection had evidence of leptospirosis.6

Wound infections also are of concern. After Katrina, 14 cases due to V. vulnificus, three of which were fatal, were recorded, as were three wound infections, with two deaths due to V. parahaemolyticus.2 More common causes of wound infection, of course, also occur.


Table 1. Infectious Diseases After a Disaster



Escherichia coli


Hepatitis B, C, and HIV


Legionnaires’ disease





Skin infections



Trench foot or immersion foot



Vibrio cholerae

Vibrio vulnificus

West Nile virus

Skin/mucosal infections identified after Katrina included MRSA infection, tinea corporis, folliculitis, and presumed viral conjunctivitis. Others observed were scabies, head lice, and immersion foot. Arthropod bites, which may mimic infection, also were observed. Varicella infection often is diagnosed first as the result of its skin manifestations.

Respiratory illnesses noted by CDC after Katrina included pertussis, respiratory syncytial virus infection, and streptococcal pharyngitis, with the apparent increased frequency likely the result of crowding in evacuation centers. Exposure to communicable diseases, including respiratory infections in these centers, is of concern and perhaps none more so than tuberculosis. CDC reported that after Katrina, evaluation of evacuees with suspected tuberculosis resulted in confirmation of this infection in two of nine. An associated problem for public health departments was assuring maintenance of patients on therapy for tuberculosis.

Crowding in shelters leads to exposure to additional communicable diseases. Among illnesses identified in Louisiana shelters after Katrina was “flu-like symptoms or pneumonia,” which occurred in 26.3/1,000 residents and was more common than all other infections (15.6/1,000).2 Among these “other infections” were tuberculosis, hepatitis, pertussis, varicella, encephalitis, meningitis, and “other serious communicable illness of outbreak concern.” Diarrhea occurred in 12.8/1,000 sheltered evacuees.

Also of concern after fresh water flooding, whether after a hurricane or not, is an increase of arbovirus infections as a result of proliferation of mosquito populations. An apparent increase in cases of West Nile virus infection was observed in Mississippi after Katrina. The recent introduction of Zika may prove to be of concern. Finally, after recession of the flood waters, molds will take over.7

The strain placed on public health by extreme weather events is enormous. Posid has listed some of the issues that must be faced.2 (See Table 2.) Dean Winslow provided a fascinating narrative insider review of the elements of the critical military response to Katrina, for which he was tasked with assessing and managing public health issues and force protection issues for the National Guard and active duty forces involved in rescue, recovery, and relief operations.8 Events such as those discussed here will only continue to increase in frequency and ferocity as climate change progresses.

Table 2. Public Health Issues Associated With Natural Disasters

Water quality


Solid waste disposal

General sanitation (debris removal)

Vector control

Immunizations (workers and population)

Close-quarter, densely populated living conditions

Disruption of access to medical services

Also — maintenance of continuity of care (HIV, TB)


  1. McMichael AJ. Extreme weather events and infectious disease outbreaks. Virulence 2015;6:543-547.
  2. Posid J. Infectious disease issues associate with Hurricane Katrina. Available at: Accessed Sept. 12, 2017.
  3. Cann KF, Thomas DR, Salmon RL, et al. Extreme water-related events and waterborne disease. Epidemiol Infect 2013;141:671-686.
  4. Centers for Disease Control and Prevention. Norovirus outbreak among evacuees from Hurricane Katrina — Houston, Texas, September 2005. MMWR Morb Mortal Wkly Rep 2005;54:1016-1018.
  5. Centers for Disease Control and Prevention. Two cases of toxigenic Vibrio cholerae O1 infection after Hurricanes Katrina and Rita — Louisiana, October 2005. MMWR Morb Mortal Wkly Rep 2006;55:31-32.
  6. Sanders EJ, Rigau-Pérez JG, Smits HL, et al. Increase of leptospirosis in dengue-negative patients after a hurricane in Puerto Rico in 1996 [correction of 1966]. Am J Trop Med Hyg 1999;61:399-404.
  7. Centers for Disease Control and Prevention. Mold after a disaster. Available at: Accessed Sept. 12, 2017.
  8. Winslow DL. Wind, rain, flooding, and fear: Coordinating military public health in the aftermath of Hurricane Katrina. Clin Infect Dis 2005;41:1759-1763.