Puerto Rico is in the midst of a prolonged humanitarian crisis after being struck by Hurricane Maria nearly one month ago. Much of Puerto Rico remains without electricity, clean drinking water, and limited gas. In addition, the US territory now faces a growing public health crisis, including increased risk of infectious diseases brought on by the conditions on the storm-ravaged island.

Dr. Rajeev Fernando, chief of infectious diseases at Stony Brook Southampton Hospital in New York, told ABC News that the number of sick people is expected to rise in the coming weeks because many infections have a 2-3-week incubation period. Specifically, this past week saw two confirmed cases of leptospirosis in Canovanas, a region on the northeast side of the island, with the CDC investigating a total of 10 suspected cases across the country. These cases, though small in number, are a significant concern for two reasons: 1) challenges to leptospirosis surveillance in general suggest the actual case count could be higher and 2) lack of medical infrastructure on the island increases the risk of infectious disease spread in the coming weeks.

Background on Leptospirosis

Leptospirosis is a bacterial infection caused by a corkscrew-shaped Leptospira bacterium. The mild form of the infection typically displays more generalizable symptoms such as headaches, muscle pain, and fever, while severe cases — also known as Weil’s disease or icteric leptospirosis — may present with pulmonary hemorrhage, meningitis, or kidney and liver failure. According to one systematic review of global leptospirosis morbidity and mortality, the worldwide case fatality rate is 5.72% (although this is believed to be an underestimate). The majority of the disease burden occurs in poor and tropical regions, particularly after heavy rain and flooding. Approximately 5%-10% of those with leptospirosis develop the severe form; the case fatality rate in those with severe disease is 5%-15%. Rodents are the primary source of infection to humans, but various wild and domestic animals can carry the bacterium. 

Transmission occurs when water contaminated with the urine of infected animals comes into contact with cuts, abrasions, or with the mucosal membranes of the eyes, nose, and mouth, or potentially through ingestion. Human-to-human transmission of leptospirosis is extremely rare; however, human infection of leptospirosis does show transient leptospiral shedding, and reports of infection have occurred through sexual transmission and lactation. Transplacental transmission may occur during pregnancy, resulting in abortion or stillbirth.

Challenges to Leptospirosis Surveillance

While the Puerto Rico Department of Health reported 729 leptospirosis cases from 1990-2014, these data likely underestimate the true burden of disease. Data from a previously released CDC MMWR report suggest that 60%-90% of fatal leptospirosis cases in Puerto Rico are not reported. There are at least three reasons for this. First, according to the CDC report, there is a “lack of timely diagnostic services,” with current methods generally considered time-consuming and requiring advanced laboratory services not typically available in remote or underdeveloped locations. Second, due to similar symptom presentation as dengue, many cases might be misdiagnosed. This is of particular concern in areas where dengue is endemic, such as in Puerto Rico. A third contributing factor to the underreporting of leptospirosis is the number of asymptomatic cases. A serologic study done on a 1995 outbreak of leptospirosis in Nicaragua found that only 29.4% of 85 seropositive patients reported febrile illness within two months prior to antibody collection.

Increased Risk of Infection

A number of factors suggest that leptospirosis cases may become more prevalent in Puerto Rico in the weeks to come. While the scientific literature concerning post-hurricane infection with leptospirosis is scarce, one survey conducted during the 1996 leptospirosis outbreak in Puerto Rico found a “more than 4-fold increase” in laboratory-confirmed cases following Hurricane Hortense, from 4 out of 72 pre-hurricane patients, to 17 out of 70 post-hurricane patients. Additionally, out of the 17 confirmed cases of leptospirosis, 16 were male patients, who were believed to be at a greater risk for infection because of their assistance in “post-hurricane relief work.”

Floodwaters also provide ideal conditions for leptospires survival. According to the above survey, flooding “prevents [infected] animal urine from being absorbed into the soil or evaporating so leptospires may pass directly into the surface waters or persist in mud.” Puerto Rico residents may contract the bacterium either by drinking contaminated floodwater or swimming with open sores.

Dr. Raul Hernandez, an internist based in San Juan, told Fox News that “due to lack of safe drinking water, people are drinking from whatever water sources they can find – rivers, creeks.” The Puerto Rico Department of Health urges people to drink only bottled water or to boil drinking water and to wear protective shoes near bodies of water that could be contaminated with animal urine. FEMA authorized $70 million to Puerto Rico to begin water restoration efforts. The challenges of responding to the public health crisis, including infectious disease outbreaks, is compounded by logistical realities. According to Puerto Rico government officials, as of October 19, over 82% of the island remains without power, over 28% of water meters are inactive, and only 36 of 65 hospitals have electricity, and even those with power may be running at limited capacity.


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: Digitally-colorized, scanning electron microscopic image revealing the corkscrew-shaped, Leptospira bacteria. 

Photo courtesy of CDC/ Rob Weyant