The timing of all infectious diseases may be seasonal

A new study from the Columbia University Mailman School of Public Health suggests that all infectious diseases are seasonal, just like wintertime influenza outbreaks. Dr. Micaela Martinez noted that chickenpox becomes most widespread in the spring, while gonorrhea and polio are most prevalent in the summer.

For the investigation, Dr. Martinez collected information from the World Health Organization, the U.S. Centers for Disease Control and Prevention, and peer-reviewed publications. Next, she constructed a calendar of epidemics for 69 infectious diseases, from rare tropical diseases to common infections.

The study revealed that acute infectious diseases like the flu are not the only conditions that can be seasonal. Chronic infectious diseases like Hepatitis B can also be expected at certain times of the year.

The results of preliminary studies have shown that even HIV-AIDS has a seasonal element, which is believed to be driven by seasonal changes in malnutrition and agriculture.

The researchers have identified four main drivers of seasonality in infectious diseases, including temperatures and other environmental factors, host behaviors such as children going to school, and seasonal biological rhythms. Finally, ecological factors such as algae play a role the outbreak of cholera.

Image Credit: Columbia Mailman School of Public Health

“Seasonality is a powerful and universal feature of infectious diseases, although the scientific community has largely ignored it for the majority of infections,” said Dr. Martinez. “Much work is needed to understand the forces driving disease seasonality and understand how we can leverage seasonality to design interventions to prevent outbreaks and treat chronic infections.”

Identifying the drivers of seasonal outbreaks is not always straightforward, but can really pay off. For example, the bacteria that cause cholera, which spread to humans by fecal-oral transmission, can be maintained in water supported by algae.

Public health officials may develop an intervention to prevent the transmission of cholera from infected individuals, or to target the bacteria surviving in algal-filled waterbodies. However, the key season to employ each of these interventions would likely be different.

The study is published in the journal PLOS Pathogens.

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By Chrissy Sexton, Earth.com Staff Writer