|Year : 2015 | Volume
| Issue : 4 | Page : 503-506
Salmonella Weltevreden food poisoning in a tea garden of Assam: An outbreak investigation
L Saikia, A Sharma, R Nath, G Choudhury, AK Borah
Department of Microbiology, Assam Medical College, Dibrugarh, Assam, India
|Date of Submission||29-Oct-2014|
|Date of Acceptance||21-Apr-2015|
|Date of Web Publication||16-Oct-2015|
Department of Microbiology, Assam Medical College, Dibrugarh, Assam
Source of Support: None, Conflict of Interest: None
Background: Salmonella enterica serovar Weltevreden has been a rare cause of acute gastroenteritis occurring worldwide. Here, we report an outbreak of food poisoning in a tea garden. Objectives: To determine the aetiological agent and risk factors responsible for the outbreak and to take necessary steps for prevention of future outbreaks. Materials and Methods: Affected area was visited by a team of microbiologists for collecting stool samples/rectal swabs from affected patients. Samples were processed by culture followed by confirmation of the isolates biochemically, automated bacterial identification system, conventional serotyping and molecular typing. Water samples were also processed for detection of faecal contamination. Antimicrobial susceptibility testing was performed by Kirby–Bauer disc diffusion technique according to the Clinical Laboratory Standard Institute guidelines. Results: The isolates were confirmed as S. enterica subspecies enterica serovar Weltevreden. They were found sensitive to ampicillin, amoxycillin-clavulanic acid, ciprofloxacin, ofloxacin, norfloxacin, cefotaxime, ceftriaxone, co-trimoxazole and doxycycline. Water samples showed high-level faecal contamination. Source of outbreak was found to be drinking water contaminated with dead livestock. House to house visit was made for early diagnosis and treatment of the cases, awareness campaigning and chlorination of drinking water. Conclusions: This report emphasises the geographical distribution of this organism in Assam. As S. Weltevreden is widely distributed in domestic animals, people should be made aware of immediate reporting of any unusual death among the livestock and their safe disposal which can significantly reduce the incidence of non-typhoidal salmonellosis in the country.
Keywords: Assam, food poisoning, non-typhoidal Salmonella, Salmonella Weltevreden
|How to cite this article:|
Saikia L, Sharma A, Nath R, Choudhury G, Borah A K. Salmonella Weltevreden food poisoning in a tea garden of Assam: An outbreak investigation. Indian J Med Microbiol 2015;33:503-6
|How to cite this URL:|
Saikia L, Sharma A, Nath R, Choudhury G, Borah A K. Salmonella Weltevreden food poisoning in a tea garden of Assam: An outbreak investigation. Indian J Med Microbiol [serial online] 2015 [cited 2020 Feb 21];33:503-6. Available from: http://www.ijmm.org/text.asp?2015/33/4/503/167347
| ~ Introduction|| |
Acute gastroenteritis caused by non-typhoidal Salmonella More Details continues to be an important public health problem worldwide. Transmission most commonly occurs due to consumption of raw and undercooked meat, poultry eggs, and dairy products. Outbreak due to contaminated drinking water is also not uncommon. The most common agent associated with non-typhoidal Salmonellosis More Details is Salmonella enterica serovar Enteritidis, Typhimurium., In recent years, outbreak caused by S. enterica serovar Weltevreden has been increasingly reported most frequently from South-East Asia.,,, However, it has not been reported before from this North-East part of India as causative agent of food poisoning in human.
We report here an outbreak of food poisoning due to S. Weltevreden, in a tea garden of an upper Assam district in the month of June, 2014. The patients presented with acute onset of vomiting or diarrhoea with or without fever with other signs and symptoms such as headache, anorexia and abdominal pain. The source of the outbreak was suspected to be drinking water contaminated with dead livestock and poor environmental sanitation as there was no history of consumption of any common food in any social gathering in the recent past. Hence, an investigation of the outbreak was carried out to determine the cause of the outbreak along with evaluation of associated risk factors for taking necessary steps to prevent future outbreak.
| ~ Materials and Methods|| |
On June 7, 2014, in the morning the information about the outbreak was received after reporting of the index case in a tertiary care hospital after referral from the tea estate on June 6, 2014 in the afternoon. The information was also received from the District Surveillance Unit simultaneously. A case was defined as one presenting with acute onset of vomiting or diarrhoea with or without fever with other symptoms such as headache, anorexia and abdominal pain. On the same day, a primary case was referred to the hospital followed by another 57 cases reported with similar symptoms on June 7, 2014. On June 7, 2014, a team of microbiologists, epidemiologists and clinicians visited the tea garden to investigate the outbreak. Relevant data were collected by interviewing the patients and health care providers and recorded in a predesigned proforma. There were 9 more cases reported on June 8, 2014 and no new cases were reported thereafter.
Rectal swab was collected in Cary Blair media from the index case on June 7, 2014 after about 9 h of onset of the symptoms. Rectal swabs were also collected from another 8 primary cases. Before starting the investigation, ethical clearance was obtained from the Institutional Ethical Committee. Informed consent was obtained from all the cases investigated.
Samples were directly inoculated on blood agar, BBL ™ MacConkey agar, xylose lysine deoxycholate agar and for enrichment in alkaline peptone water and Selenite F broth and incubated at 37°C. Culture media were procured from Becton, Dickinson and Company, Sparks, USA and HiMedia Laboratories Private Ltd., Mumbai. The isolates were confirmed biochemically, by VITEK 2 Compact 30 Bacterial identification system version 7.01 (bioMerieux Inc, Durham, USA), by conventional serotyping and molecular typing. Antimicrobial susceptibility testing was performed by Kirby–Bauer disc diffusion technique according to the Clinical Laboratory Standard Institute guidelines using commercial discs from HiMedia Laboratories Private Ltd., Mumbai.
Water samples were collected from six tube wells (drinking water sources) of the households of the primary cases including the index case under sterile conditions. Samples were processed by multiple tube test for total coliform (presumptive coliform count), confirmed Escherichia More Details coli count and culture was done for detection of S. Weltevreden.
Food sample was not collected because none of the affected patient gave history of consumption of any common food in any social gathering. The incident was considered as an outbreak because it was caused by an agent not previously recognised in this region affecting a large group of the population at the same time in the same geographical region. The outbreak was controlled after 3 days of its onset.
| ~ Results|| |
Of the 284 subjects, 72 individuals were affected in this outbreak involving 40 households. The attack rate was 25.3%. The affected population comprised of 30 males and 42 females. The age range of the patients was 1.5–65 years; median: 25 years. Totally, 21 of them were children below 14 years.
The isolates were identified as S. enterica subspecies enterica conventionally and in bioMérieux's VITEK ® 2 Compact 30 Bacterial identification system (7.01). The isolates agglutinated with group specific Salmonella poly 'O' (A–G) antiserum (DENKA, SEIKEN, Tokyo, Japan), but not with type specific flagellar antisera of Salmonella typhi, Salmonella paratyphi A, S. paratyphi B and hence, reported as S. enterica subspecies enterica. The isolates were found sensitive to ampicillin, amoxycillin-clavulanic acid, ciprofloxacin, ofloxacin, norfloxacin, cefotaxime, ceftriaxone, co-trimoxazole and doxycycline and were resistant to amikacin. The isolates were confirmed as S. enterica subspecies enterica var Weltevreden (S. Weltevreden 3, 10:R: Z6) in National Institute of Cholera and Enteric Diseases (NICED), Kolkata by conventional serotyping. Multiplex polymerase chain reaction-based genotyping and virulence typing [Table 1] and [Figure 1] were also done at College of Veterinary Sciences, Assam Agricultural University, Khanapara, Assam. The origin of the strains as shown in [Table 1] for genotyping of Salmonella are: STM (4525, 2150, 0311, 3845, 0171, 0716, 2771, 4538, 0839, 3518, 1350, 1608) is S. enterica subsp. enterica serovar Typhimurium LT2, GenBank accession number: AE006468 (the strain was first isolated in 1940 and has been maintained as ATCC 700720); STY (2296, 2349, 0345) is multiple drug resistant S. enterica subsp. enterica serovar Typhi strain CT18, GenBank accession number: AL513382 (isolated from patient); sdf I is S. enterica subsp. enterica serovar Enteritidis specific sequence I, GenBank accession number: AF370707 (isolated from environment, creek). The genes reported in [Figure 1] are present in other serotypes of Salmonella also.
|Table 1: Multiplex PCR based genotyping of Salmonella enterica subsp. enterica|
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|Figure 1: Detection of virulence genes of Salmonella Weltevreden by multiplex polymerase chain reaction Lane 1: 100 base pair DNA ladder, Lane 2: S. Weltevreden showing presence of inv A (942 bp), stn (543 bp), sop B (470 bp), inv H (305 bp) and sop E (254 bp)|
Click here to view
Water samples collected from various sources of drinking water showed high-level faecal contamination in all the samples with most probable number of bacteria per 100 ml is as high as 95 and confirmed E. coli count was as high as 1600/100 ml. Similar isolates were also obtained from all the water samples that were confirmed as S. enterica subspecies enterica var Weltevreden.
The patients were treated with ofloxacin intravenously (200 mg twice daily for 3 days), intravenous and oral rehydration therapy. All the patients responded to the treatment without any death. The total number of laboratory confirmed primary cases were 9; total number of probable primary cases were 63 and number of estimated total primary cases were 72.
The observation of this outbreak investigation was that, there was no history of consumption of any common food in any social gathering. All the patients had their food in their own house during last 7 days prior to the onset of the outbreak. According to the report of the local people, the poultry chickens of that area suffered from some unknown disease causing death of many chickens which were later on thrown into a pond for disposal. Also, there was flood 2 days prior to onset of the outbreak leading to over flowing of pond water into the drains and then to the residential area and tube wells which are the most common source of drinking water of that area. All houses and platforms of the tube wells of that area were "Kutcha" (made of mud) causing entry of this contaminated water into the houses as well as to the drinking water sources. There was no system for purification of drinking water in all the households. All the 72 cases of similar illness were found to be epidemiologically linked to a common water exposure. Hence, the available evidences give us the clue to suspect that, contaminated drinking water may be the source of this outbreak.
| ~ Discussion|| |
Salmonella enterica is one of the most common causes of bacterial gastroenteritis worldwide and is often implicated in food-borne outbreaks. S. enterica serovar Weltevreden is a rare cause of gastroenteritis occurring worldwide and was reported to be a serotype of increasing public health importance in India in the early 1970s., Its presence among domestic animals in India may have continued to cause human gastroenteritis.
The outbreak was controlled after 3 days of its onset by taking measures like house to house visit for awareness campaigning with involvement of the local health care providers, motivation to use boiled water for drinking, cleaning of the drains, distribution of chlorine tablet for chlorination of drinking water sources, early diagnosis and referral of the cases to tertiary care hospital and distribution of oral rehydration solutions among the affected population. There was no new case reported after the report of the last case on June 8, 2014.
This outbreak investigation has some limitation as the cause of the death among the livestock population in that area could not be evaluated because of delay in reporting the incident which could have helped in understanding the exact mode of transmission of this outbreak.
In Assam, outbreaks in tea garden with enteric pathogens are not uncommon. As these tea gardens are run by private sector, a strong commitment from these tea garden owners along with other relevant sectors to supply safe drinking water and to take necessary steps for environmental sanitation is highly recommended for prevention of large outbreak in the future.
The results of the outbreak investigation described in this paper suggest that S. Weltevreden could be associated with a waterborne outbreak in Assam in contrast to the other reported outbreaks of mostly food origin in other parts of India.,, It emphasises the necessity of a better knowledge of the epidemiology of this serovar in humans and in animals in this area to identify the probable sources of transmission. Hence, it is necessary to improve our surveillance system with collaboration between epidemiologists, clinicians, microbiologists and veterinarians for future outbreak investigations.
| ~ Acknowledgments|| |
We gratefully acknowledge Dr. Prabodh Borah, Professor of Microbiology and Head (Incharge), Animal Biotechnology, College of Veterinary Sciences, Assam Agriculture University, Assam and NICED) for confirmation of the isolate.
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