Cholera is an acute diarrhoeal disease caused by vibrio cholerae 01 or 0139.(1) cholera outbreaks are not uncommon in India. Surveillance data reveal a steady increase in reported cholera outbreaks throughout the country from 1997 to 2006, 68 outbreaks were reported, while the reported outbreaks rose to 559 between 2009 and 2017(2). Cholera may lead to death due to hypovolemic shock within 24 hours due to profuse watery diarrhea and vomiting. In most parts of the world, vibrio cholerae El tor biotype is the main cause of the outbreaks, which causes mild and asymptomatic diarrhea as compared to the classical type toxigenic strains of vibrio cholerae belonging to the O1 and O139 serogroups cause a devastating type of diarrhea. (3)

Despite the long history of cholera in India, it remains an unaddressed problem and the country continues to rank high among endemic countries (4). This disease has major historical and public health importance. It may spread like a wild fire in a community with overcrowding, poor sanitation and poor-hygiene.(1) it underlines the importance of detail study of each outbreak which can help policy makers to prevent such future occurrences. (5-7) here we are reporting an outbreak of Diarrhea caused by vibrio cholerae.

Nerli is a nearby village approximately 8-10 km away from Nanded district of Maharashtra. People from this village suddenly started complaining of loose motions vomiting, diffuse abdominal pain, fever and headache on 29th of September 2024. Patients started to arrive with these complains to Nerli sub-centre. Stable patients were treated with ORS and antibiotics; whereas patients with signs of dehydration, old age and children were referred to civil hospital and govt medical college; few got admitted to private hospitals also. Many patients reported to have symptoms.

Study Site

The present outbreak investigation was conducted in the peripheral region of Nanded, Maharashtra. The study included all patients clinically suspected of cholera during the outbreak period who presented with acute watery diarrhea. Stool samples, rectal swabs, or vomitus were collected from patients admitted to various healthcare facilities, including private hospitals, the District Civil Hospital, and the Government Medical College. Due to the involvement of multiple centers, there was no uniform protocol followed for sample collection.

Inclusion criteria

All patients presenting with acute watery diarrhea and clinically suspected cholera during the outbreak period.
Exclusion criteria

Patients with diarrheal illness due to known non-cholera etiologies or those who refused to provide samples.

A total of 115 clinical samples were received in the microbiology laboratory. Of these, 93 (80.9%) were stool samples, 18 (15.7%) were rectal swabs, and 4 (3.4%) were vomitus samples. All samples were subjected to hanging drop examination to observe darting motility suggestive of Vibrio cholerae. Following this, enrichment was done using alkaline peptone water, and samples were inoculated onto Blood agar, MacConkey agar, and TCBS (Thiosulfate-Citrate-Bile-Salt-Sucrose) agar plates for isolation.

Biochemical tests were conducted as per standard protocols. All suspected Vibrio cholerae isolates were subjected to further differentiation using Polymyxin B (50 units) and Voges-Proskauer (VP) test to identify Eltor and classical biotypes. Serotyping was done using specific anti-sera to confirm Vibrio cholerae O1 Ogawa.

Antimicrobial susceptibility testing (AST) was performed on all confirmed isolates using the Clinical and Laboratory Standards Institute (CLSI) guidelines M100, 2024. The strains were tested for sensitivity to commonly used antibiotics, and results were uniformly reported.

Sample size calculation

Was performed using the formula
n = 4pq/d²,
where p was the estimated prevalence from previous local outbreaks (taken as 20%), q = 100 - p, and d was the allowable error (taken as 8%). The minimum calculated sample size was 100, but 115 samples were collected during the outbreak, thus fulfilling the statistical requirement.

Statistical analysis

Was carried out using Microsoft Excel 2019 and Epi Info version 7.2. Results were expressed in terms of numbers and percentages for demographic and microbiological findings

Total 115 patients line listed for outbreak. Out of it 42 (37%) were females and 73 (63%) were males.

Table 1: Sample positivity

All the strains were confirmed by Anti-sera. With the anti-sera it turned out to be Vibrio cholerae O1 ogawa. All the isolates were positive for acetoin production (Voges Proskauer test positive). All the strains were sensitive to polymixin B (50U). All of them showed heamodigestion on blood agar. All these features suggest it is variant Eltor strain. All strains showed same AST pattern.

Table 2: Drug Sensitivity Testing Report

They were sensitive to Ampicillin, Norfloxacin, Tetracycline, Azithromycin and resistant to cotrimoxazole. [Table 2] Mortality reported from this outbreak is zero. No occurrence of any death (0%).

In India sporadic cases of acute diarrhea occur frequently  throughout the year. However, at times explosive outbreaks of diarrhea occur due to cholera.(3) If not taken care it can be converted into epidemics and pandemics. History of cholera dates back to 18th Century when John Snow diagnosed a cholera outbreak in London city by pure epidemiological observation of contaminated hand-pump water supply.(1) Most of the outbreaks of cholera  still follow the same route of transmission. As per the IDSP surveillance data water born outbreaks contribute to 62% of the cholera outbreaks.(2) In our study well from which water supply was provided to the village was found to be contaminated. Though Vibrio cholerae was not isolated from the well, Coliform count was found to be unacceptable; also periodic cleaning and chlorination of well was not documented. We have observed that the people having own borewell and hadn't use well water remained unaffected.

In our study, a total of 115 cases were line-listed during the cholera outbreak, with males comprising 63% and females 37%, and 45% of patients were children under 12 years, indicating a substantial pediatric burden. Vibrio cholerae was isolated from 24 samples (20.9%), with 14 positive stool cultures and 10 rectal swabs, while vomitus samples were all negative. All isolates were confirmed as Vibrio cholerae O1 Ogawa, El Tor variant, characterized by positivity for the Voges-Proskauer test, hemolysis on blood agar, and sensitivity to polymyxin B—features consistent with the classical traits of the El Tor variant.

Antimicrobial susceptibility testing revealed all strains were sensitive to Ampicillin, Norfloxacin, Tetracycline, and Azithromycin, but resistant to Cotrimoxazole. These findings are in contrast with those of Kulkarni and Chillarge (8), who in their study at a tertiary care center in Bidar (2012–2015), reported multidrug-resistant Vibrio cholerae, with resistance to Ampicillin and Nalidixic acid, while retaining sensitivity to Tetracycline, Ofloxacin, Ciprofloxacin, and Gentamicin (Kulkarni and Chillarge (8)). Similarly, BB Pal et al (9). investigated a large cholera outbreak in Kendrapada district, Odisha, and reported V. cholerae O1 Ogawa biotype El Tor strains that were resistant to Ciprofloxacin, Cotrimoxazole, Chloramphenicol, Ampicillin, and Nalidixic acid. Their isolates also possessed virulence genes (ctxA, tcpA) and belonged to the El Tor variant with the classical ctxB gene, indicating the emergence of highly virulent and resistant strains [BB Pal et al (9)]. In contrast, the isolates from our outbreak retained susceptibility to key antibiotics, such as Tetracycline and Azithromycin, indicating a favorable antimicrobial profile for current clinical management. However, the resistance to Cotrimoxazole aligns with national trends, as highlighted by Chatterjee P et al. (10), who in their scoping review identified a rising incidence of antibiotic-resistant cholera outbreaks across India. Their review, which covered 559 cholera outbreaks between 2009 and 2017, emphasized that states like Odisha, Maharashtra, and West Bengal accounted for the majority of ABR outbreaks and stressed the importance of antibiotic stewardship, effective surveillance, and the potential role of oral cholera vaccines in outbreak control (Chatterjee P et al.) (10).

The zero-mortality observed in our outbreak reflects effective clinical and public health response, including timely diagnosis, fluid management, and appropriate antimicrobial use. Many other studies have reported declining mortality due to cholera due to better healthcare services. (11-13) Nonetheless, the emergence and spread of El Tor variants with classical virulence features and varying resistance patterns highlight the critical need for sustained surveillance, rational antibiotic use, and integrated control strategies including water sanitation, hygiene (WASH), and targeted vaccination in endemic and outbreak-prone regions(15). 

The cholera outbreak in the peripheral region of Nanded, Maharashtra, predominantly affected males and a substantial proportion of the pediatric population under 12 years of age. Out of all clinical samples tested, Vibrio cholerae was isolated in a limited number, primarily from stool and rectal swabs, while none of the vomitus samples showed any growth. All strains were confirmed as Vibrio cholerae O1 Ogawa serotype and exhibited characteristics of the Eltor biotype, including positive acetoin production, sensitivity to polymyxin B, and haemodigestion on blood agar. The isolates showed uniform antibiotic sensitivity patterns—sensitive to commonly used antibiotics like Ampicillin, Norfloxacin, Tetracycline, and Azithromycin, and resistant to Cotrimoxazole. Importantly, there were no deaths reported during the outbreak, reflecting a zero mortality rate.

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