Indian Pediatrics 2004;41:912-916

An Outbreak of Hospital Acquired Diarrhea Due to Aeromonas sobria

Six children admitted in a 18 bedded hematology-oncology unit, developed acute diarrhea in a four week period between March and April 2001.Aeromonas sobria was isolated from the stool samples of these children. Salmonella senftenberg was the additional pathogen in the stool sample of one patient who developed cola coloured urine and pneumonia in the course of his illness. All the Aeromonas strains had a similar biotype and antibiogram. The diarrhea subsided spontaneously in two children whilst three responded to antimicrobial therapy. One patient sought discharge and did not return for a follow up. Aeromonas sobria with a similar profile as the isolates from the patients could be isolated from only one of several environmental sites. The outbreak could be contained by appropriate interventional measures.

Key words : Aeromonas, Diarrhea, Hospital acquired, Outbreak.

Aeromonas species are ubiquitous water borne micro-organisms. They have been reported to cause various illnesses in humans such as wound infections, septicemia, peritonitis, pneumonia, etc. They are being increasingly recognized as an important cause of diarrhea worldwide(1). Information regarding nosocomial outbreaks due to this pathogen is scanty. In this communication we describe our experience of managing an outbreak of Aeromonas species diarrhea in a pediatric hematology-oncology unit of a tertiary care center in north India.

Subjects and Methods

Six children admitted in the hematology oncology unit of Advanced Pediatric Center, PGIMER, Chandigarh developed acute diarrhea in a four-week period in March-April 2001. The clinical profile of these cases is summarized in Table I.

Table I

Clinical Profile of the Patients.

	Age	Sex	Diagnosis	Date of admission	Date of diarrhea	Treatment	Outcome
A	4 mo	M	Cyst Liver	27/03/2001	27/03/2001	Cip,Ak IV fluids	Diarrhea subsided
B	1 yr	M	Neuroecto- dermal tumor	10/04/2001	12/04/2001	Cip, Ak, Met IV fluids	Diarrhea subsided
C	3 yr	M	ALL	7/04/2001	13/04/2001	Cip, Ak, Met IV fluids	Diarrhea subsided
D	6 yr	F	ALL	11/04/2001	14/04/2001	Cip, Ak, Met IV fluids	Outcome not known
E	3 yr	M	NHL	20/04/2001	22/04/2001	ORS	Diarrhea subsided spontaneously
F	7 yr	M	Nutritional anemia	21/04/2001	23/04/2001	ORS	Diarrhea subsided spontaneously

IV fluiids – Intravenous fluids; Cip–Ciprofloxacin; Ak–Amikacin; Met  Metronidazole; 
ORS–Oral rehydration solution; ALL–Acute lymphatic leukemia; NHL –Non Hodgkins
lymphoma.

Patients’ isolates

The blood and stool samples of these patients were processed in the medical microbiology laboratory. Stool samples were collected in sterile McCartney bottles and rectal/fecal swabs in Cary Blair transport medium. The samples were processed within two hours of collection. These were inoculated onto MacConkey agar, xylose lysine deoxycholate agar, thiosulphate citrate bile salt agar and enrichment media such as Salmonella shigella broth and alkaline peptone water. Blood cultures were taken in the bile and trypticase soy broth. The suspected pathogens were identified by standard bacteriological techniques. Presumptive identification of Aeromonas was made on the basis of oxidase positivity, resistance to vibriostatic agent O/129(oxoid 10 &150 µg/disk, growth on nutrient medium containing no added salt, and negative string test. The isolates were subsequently characterised by a battery of biochemical tests(2). Follow up rectal swabs /stool swabs of these patients were taken again after an interval of one week. Rectal swabs/stool samples of other children admitted in the same ward were taken simultaneously to determine carriage.

Environmental isolates

Samples were taken from several sites in the ward. These included water from all the taps(8) and aquaguards(10), intravenous fluids and other drugs being administered to the patients(16), food samples including milk (18), swabs from the sinks(8), refrigerators (6), medicine trolleys and trays(6), utensils(18), nebulisers(6), humidifiers(4) and other equipment(6) being used by the patients.

Antimicrobial susceptibility testing

The strains were tested for antimicrobial susceptibility by Stoke’s disk diffusion method(3) using Mueller Hinton agar and antibiotic disks procured from Hi-Media laboratories, India. The following disks were used: amoxycillin (10 µg), nalidixic acid (30 µg), ciprofloxacin (1 µg), ofloxacin (5 µg), gentamicin (10 µg), amikacin (30 µg), cotrimoxazole (25 µg), chloramphenicol (30 µg), furoxone (30 µg). The plates were incubated at 37ºC overnight. The diameter of zone of inhibition of each antimicrobial agent was compared with the control (Escherichia coli NCTC 10418) and recorded as resistant, sensitive or intermediate(3).

Results

Out of the 18 children in the hematology oncology ward during the period of outbreak, six children developed diarrhea. The age of the affected children (5 males & 1 female) ranged from 4.5 months to 7 years. They were receiving treatment for their underlying diseases. Two children were neutropenic at the time of development of diarrhea. The index case, a four and a half month child, was admitted on 27 March 2001 with symptoms of acute watery diarrhea and fever. Five more children admitted in the same ward developed diarrhea (4 acute watery diarrhea and a solitary case with bloody diarrhea). The mean post admission day for development of diarrhea was 2.7 days. The child who presented with bloody diarrhea later developed cola colured urine and pneumonia.

Aeromonas species was the sole enteropathogen isolated in 5 patients. One had mixed infection with Aeromonas and Salmonella senftenberg. All strains produced acid and gas from glucose, produced indole, decarboxylated lysine and arginine, produced acetoin in Voges Proskauer test, produced acid from L-arabinose, sucrose and mannitol and were resistant to ampicillin (10 µg). The antimicrobial susceptibility pattern of these isolates showed that all the strains were sensitive to amikacin, chloramphenicol, furoxone and resistant to ampicillin, cotrimoxazole, nalidixic acid and ciprofloxacin. The diarrhea was self-limiting in two patients while four patients were treated with ciprofloxacin, amikacin and metronidazole. Five children recovered uneventfully while the outcome of one patient who had developed pneumonia is not known since the child was taken home against medical advice. Rectal/fecal swab cultures of other admitted children not having diarrhea were negative for enteropathogens. Aeromonas could not be isolated from follow up rectal swab cultures of children with diarrhea.

On environment sampling, Aeromonas sobria could be isolated from one sink that was being used by the patients’ attendants for washing utensils. All other cultures were negative for Aeromonas species. The strain from the environment was similar to the clinical isolates from the patients in biochemical reactions and antimicrobial susceptibility patterns.

Discussion

Aeromonas are ubiquitous bacteria and their prevalence is particularly high in a variety of aquatic environments including drinking water, estuaries, sewage etc. and numerous food products. Aeromonas species has been reported as an important cause of acute diarrhea in children and adults(2). The overall incidence of Aeromonas species in diarrheal diseases varies from 1 to 27%(4-5). The most commonly implicated species are A. hydrophila, A. sobria, and A. caviae. Though commonly associated with diarrheal disease in healthy adults, they can cause serious infections in immuno-compromised patients(6). Nosocomial infections appear to be uncommon and only one outbreak of hospital-acquired infection has been previously reported(7). A few outbreaks of water or food borne Aeromonas species diarrhea have been documented(8,9).

The present outbreak evolved over a period of one month. Aeromonas is sporadically isolated in our geographic area. The outbreak was suspected only when clustering of cases was observed from the same ward. It is a well-established fact that infections due to Aeromonas are more severe in immunocompromised individuals. In our study, five of the affected children had acute watery diarrhea of moderate to severe degree. Only one child who was co-infected with Salmonella senftenberg presented with bloody stools, cola colored urine and later on developed pneumonia. However, both these organisms have the potential to cause invasive disease and hemolytic-uremic syndrome.

All the isolates were A. sobria belonging to the same biotype and had similar antimicrobial profile. The single environmental isolate of Aeromonas sp had the same biotype and antibiogram. Aeromonas species are known to reside in a large variety of aquatic environments. Though we could isolate Aeromonas sobria from one of the sinks, it is not sure whether the sink acted as a source of infection or was simply contaminated with the organisms. The outbreak evolved over a period of one month, which suggests person-to-person transmission and practically rules out point source outbreak. The following interventional measures were taken: the patients were isolated, barrier nursing was instituted and the sinks were disinfected. The patients’ attendants, nurses and doctors were instructed to wash their hands before handling the patients. The caretakers were counselled to wash their hands and clean the utensils properly before feeding the children. These measures controlled the outbreak. The organism has not been isolated in culture specimens since April 2001.

Contributors: NT and SK were involved in identification, investigation, reporting of the outbreak and preparation of the manuscript; AT and RKM provided the clinical details; MS provided the facilities for investigations. NT will be the guarantor of the paper.

Funding: Postgraduate Institute of Medical Education and Research, Chandigarh.

Competing interests: None stated.

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