By Ethan Covey
During a 15-week period following the landfall of Hurricane Fiona, cases of leptospirosis spiked in Puerto Rico, reaching levels more than 3.5 times the norm (MMWR Morb Mortal Wkly Rep2024;73[35]:763-768).
Leptospirosis, which is an acute bacterial illness, occurs year-round in Puerto Rico, with reported cases increasing after heavy rainfall and flooding. Approximately 10% to 15% of leptospirosis patients progress to severe, potentially fatal illness.
“Identifying leptospirosis early and treating patients with recommended antibiotics are critical to reducing illness and death associated with leptospirosis,” said Forrest K. Jones, PhD, an epidemiologist with the CDC’s Dengue Branch in San Juan.
The report documented an outbreak of leptospirosis after flooding resulting from Hurricane Fiona, which made landfall on Sept. 18, 2022. During the 15 weeks after the hurricane, 156 patients experienced signs and symptoms of leptospirosis and had a specimen with a positive laboratory result reported to the Puerto Rico Department of Health (PRDH). The mean weekly number of cases during this period was 3.6 times higher than the weekly number of cases during the previous 37 weeks (10.4 vs. 2.9). Weekly case numbers remained elevated through September 2023.
The proportion of people with leptospirosis who reported exposure to potentially contaminated water increased from 11% to 35% after the hurricane. Testing and healthcare provider awareness of leptospirosis also increased—facts that likely contributed to the jump in cases, according to the epidemiologists.
“The report describes the proactive public health response undertaken by the PRDH and CDC, highlighting the importance of strengthening epidemiological surveillance, ensuring access to laboratory testing and raising the awareness among clinicians and the public,” Dr. Jones said. “These actions can help reduce illness and death by enhancing the identification of cases to allow for early antibiotic treatment. In areas where leptospirosis is found, health departments can streamline suspect case reporting and laboratory testing as well as proactively communicate with healthcare providers to improve case identification.”
This is important, Dr. Jones added, because “early leptospirosis detection and treatment are key to reduce illnesses and deaths. Clinicians should initiate antibiotic treatment as soon as possible in patients with high clinical suspicion of leptospirosis.”
Future research may help clarify what types of exposure to potentially contaminated water occur in people who develop leptospirosis after hurricanes.
“Studying types of exposure may be able to further elicit risk factors and help guide preventative messaging,” he said.
In addition, he added that it could be helpful to clarify how many of the cases detected during the outbreak were due to increased exposure in the environment and how many were due to increased suspicion and testing for leptospirosis after the hurricane, as well as how serological screening tests should be deployed to maximize detection of acute infections while minimizing detection of prior infections in endemic areas.
The effects of climate change may increase the risk for similar outbreaks in other areas as extreme weather spreads, Dr. Jones added.
“More frequent and more intense extreme weather events that cause floods could cause leptospirosis cases to increase in the U.S.,” he said.
Dr. Jones reported no relevant financial disclosures.
