Why Shigella Spreads Quickly During the Monsoon Season, Expert Explains

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Every year, as the monsoon rains arrive, hospitals and clinics across witness a predictable but alarming surge in cases of acute diarrhoeal illness. There are many pathogens that cause an increase in these infections, but one of them - Shigella, the causative agent of bacillary dysentery stands out because of its ability to spread so quickly and actively. It is important to understand this process.

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We spoke to Dr Gopakumar, MD, Senior Consultant and HOD, Internal Medicine, Apollo Adlux Hospital, Angamaly, Kerala, who explained why Shigella spreads quickly during the monsoon season.

What Is Shigella?

Shigella is a type of gram-negative bacterium that leads to shigellosis through infection of the colon. "The signs include bloody and mucoid diarrhoea, stomach pains, and fever. What makes Shigella bacteria very dangerous is the low infectious dose, which ranges from 10 to 100 bacteria. This is in stark contrast to many other gut pathogens that require millions of organisms to establish an infection," explained Dr Gopakumar.

Rising Number of Shigella Cases During Monsoon

Monsoon season creates a near-perfect storm of conditions that favour the rapid dissemination of Shigella. These include:

Contaminated Water Sources

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Rainy seasons lead to surface run-off, which carries faeces into the open wells, bore wells, and tanks in which water is stored by the community. "When water distribution systems are overloaded, contaminated water enters homes. Shigella can survive in water for several hours or days, meaning that a single lapse is enough to infect an entire neighbourhood," said Dr Gopakumar.

Flood and Sanitation Failure

Flooded roads and areas result in sewage overflow, thus polluting water and food resources. This failure of sanitation facilities in urban and semi-urban areas results in faecal-oral transmission, which is the most common method of Shigella transmission.

Transmission by Flies

The monsoon period sees a tremendous rise in the number of flies, which reproduce abundantly in the rainy, organic debris. "The flies act as mechanical carriers; they alight on contaminated faeces and later on food, carrying the Shigella quite efficiently. As the infective dose is low, a minimal infection from a fly can produce disease," added Dr Gopakumar.

Transmission from Person to Person

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Transmission of Shigella occurs with extreme ease through person-to-person mode. A person infected by the bacteria, if fails to clean their hands properly after visiting the toilet, can transmit the infection through contaminated food or objects. In the monsoon, when people congregate inside their houses, this mode increases significantly.

Which Individuals Are at Risk?

"Children aged five years and below are the most vulnerable group affected by shigellosis because their immunity is still being developed, and they cannot practice proper hand washing practices. The elderly, malnourished individuals, and those with underlying health conditions are also at heightened risk for severe disease and complications such as haemolytic uraemic syndrome, a serious condition affecting the kidneys," warned Dr Gopakumar.

Prevention Is The Best Defence

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The good news is that Shigella infection is largely preventable. "Rigorous handwashing with soap and water, particularly before meals and after using the toilet, remains the single most effective individual measure. Drinking only boiled or properly purified water, avoiding raw or cut fruits and vegetables from roadside vendors during the monsoon, and ensuring food is freshly prepared and covered are equally critical steps," advised Dr Gopakumar.

Message From The Expert

Dr Gopakumar concluded, "Early identification and rehydration become crucial. It is advised to use antibiotics in proven or presumptive cases of shigellosis, although the type of antibiotic should depend on local resistance, since there have been many reports of resistance in Shigella bacteria. In case you or a relative suffers from watery or bloody diarrhoea along with fever during the rainy season, do not hesitate to seek medical attention."

A few key practices to keep in mind include drinking clean water, washing hands regularly, and seeking medical attention promptly.

Disclaimer: The information provided in this article is for general informational and educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or a qualified healthcare provider with any questions you may have regarding a medical condition.