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Kerala's Shigella outbreak continues to widen, with the state reporting eight more infections as of June 26, taking the number of cases recorded this month to 180. The Health Department said six deaths linked to the highly infectious bacterial disease have been reported in June, while the total number of confirmed cases this year has climbed to 256, prompting heightened surveillance across affected districts.
Of the eight newly reported cases, three were detected in Kozhikode, two in Wayanad, and one each in Ernakulam, Thrissur and Malappuram. Health officials have intensified monitoring and disease-control measures as cases continue to emerge from multiple parts of the state.
Shigella is a highly infectious Gram-negative bacterium that causes shigellosis, or bacillary dysentery, an intestinal infection characterised by bloody diarrhoea.
Medical experts say that although Kerala has one of India's strongest public health systems, changing environmental conditions, including rapid urbanisation, deteriorating water quality, inadequate sanitation, and overcrowding, have increased the state's vulnerability to outbreaks of communicable diseases such as shigellosis.
No new variant, but sanitation remains critical
The Kozhikode District Medical Officer (DMO), Dr KK Rajaram, said no new guidelines have been issued following the recent rise in shigellosis cases, as the situation continues to be closely monitored by the Health Department and the Disease Control wing.
"There is no evidence of the emergence of any new bacterial variant other than the currently circulating Shigella strain in the region," the DMO told TNM.
"The Health Department is continuing with the standard preventive measures already in place. Our field teams are carrying out routine surveillance for waterborne diseases and extensive water quality testing in affected areas. At the same time, awareness campaigns are being conducted to educate the public on maintaining sanitation, practising proper hand hygiene, and consuming only safe drinking water. We are closely monitoring the situation and will take additional measures if required," he added.
Dr Anish, a researcher at the Kerala One Health Centre for Nipah Research and Resilience, said shigellosis is a form of bacterial dysentery and, although classified as a waterborne disease, it differs significantly from classical waterborne infections such as cholera.
"Shigella does not require a high bacterial load to cause infection. While diseases like cholera need heavily contaminated water for transmission, Shigella can spread with only minimal contamination," he told TNM.
"It can also be transmitted through food contaminated by flies and poor personal hygiene, making community transmission much easier." He explained that the bacterium exists in four major serotypes, Shigella dysenteriae, Shigella flexneri, Shigella sonnei and Shigella boydii.
According to him, S. dysenteriae, which is associated with the most underdeveloped and unhygienic settings in Asia and Africa, has the highest fatality rate among the four serotypes. However, as communities gain better access to healthcare and sanitation and develop greater herd immunity, the dominant circulating strain tends to shift towards S. sonnei, the serotype more commonly found in Europe and North America.
"The predominant strain circulating in Kerala today is Shigella sonnei, reflecting this epidemiological transition," he said, adding that Kerala's disease profile itself is changing, with infections such as shigellosis and norovirus increasingly resembling patterns seen in developed countries, while diseases such as typhoid continue to be more common in developing nations. He also noted that identifying Shigella serotypes requires specialised laboratory testing by trained microbiologists because each serotype demands different diagnostic methods.
Dr Anish said there is currently no widely available, sustainable vaccine against shigellosis, unlike many viral diseases where vaccines provide long-term protection. "Developing effective vaccines against bacterial infections is far more challenging because they require different dosing strategies and do not produce the same long-term immune response as viral vaccines," he said, adding that treatment depends on targeted antibiotics selected according to the susceptibility of the infecting strain, although recovery is not determined by medication alone.
Stressing that prevention remains the most effective strategy, he said the disease can only be contained through safe drinking water, improved hygiene and better sanitation. "Kerala has traditionally been successful in controlling waterborne diseases, but lifestyle changes have altered exposure risks. Earlier, people routinely consumed boiled and cooled water, but today, many rely directly on filtered water, which is safe only if filtration systems are properly maintained," he said.
He also warned that ageing or damaged household septic tanks could leak and contaminate groundwater, while untreated domestic and hospital sewage could further contribute to the spread of infection. "Kerala needs an efficient, centralised sewage treatment system where wastewater is properly treated before disposal. At the same time, improving personal hygiene and community sanitation practices is essential to prevent the spread of Shigella," he said.
This article was written by a student interning with TNM.
