Aeromonas salmonicida is a well-known pathogen in salmonid fishes. It was believed to be non-pathogenic to humans because of inability to grow at 37°C. Here we present a case of a woman in her 20s who was diagnosed with abdominal tuberculosis 6 months previously but had not been compliant with the treatment. She presented with occasional febrile episodes, whitish vaginal discharge, burning micturition, anal ulcer, whitish discharge from mouth and recent onset breathlessness. Patient tested serologically positive for HIV-1, and A. salmonicida was isolated from urine sample. Patient was treated with antituberculosis therapy, antiretroviral therapy and antimicrobials. She showed marked improvement over the next few weeks. This case highlights the importance of recognition of rare organisms, especially in immunocompromised patients. The identification and subsequent treatment of such pathogens have improved since the advent of automated identification systems.
- HIV / AIDS
- Tropical medicine (infectious disease)
- Urinary tract infections
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Organisms belonging to genus Aeromonas are facultatively anaerobic gram-negative rods that are oxidase-positive and are widely distributed in the natural environment.1 Aeromonas salmonicida is a well-known pathogen in salmonid fishes. It is generally non-motile and grows optimally at 22°C–28°C.2 It was believed to be non-pathogenic to humans because of inability to grow at 37°C. However, a handful of cases have been sporadically reported over the past three decades, which may be attributed to a subset of strains within the species having ability to grow at 35°C–37°C.3
Here we present a case of a newly diagnosed AIDS patient where A. salmonicida was isolated from urine.
A woman in her 20s, from central India, presented to the emergency department with complaints of occasional febrile episodes for the last few years which had increased in frequency over the last 6 months, whitish vaginal discharge with itching over the last 6 months, lower abdominal pain and amenorrhoea over the last 6 months, cough with expectoration, shortness of breath, burning micturition, anal ulcer and whitish discharge from mouth since the last 2 months. She was diagnosed with abdominal tuberculosis 6 months ago on the basis of abdominal ultrasonography showing multiple necrotic lymph nodes and started on antituberculosis treatment. She had not been compliant with the treatment regimen initially but was on regular treatment for last 2 months with continuation phase. The reason for this hospital visit was enhanced breathlessness and burning micturition for 5–7 days.
At the time of admission, she was conscious, oriented and grossly emaciated in appearance with generalised muscle wasting and hyperpigmentation on palms and soles. Pallor was evident but there was no icterus, cyanosis, clubbing, lymphadenopathy or pedal oedema. Pulse rate was 102 beats per minute, oxygen saturation was 76% (improved to 96% with 0.5 L oxygen), blood pressure was 80/60 mm Hg, random blood glucose was 104 mg/dL, and she was afebrile. Oral thrush was observed over dorsum of tongue, buccal mucosa and soft palate. On respiratory auscultation, bilateral coarse crepts were heard in mammary, axillary and infra-axillary areas, with increased intensity in the left lung. On palpation, abdomen was soft and non-tender without any organomegaly and bowel sounds were present. Perianal skin was normal in appearance except for circumferential maceration at anal verge with no pus discharging points. Digital rectal examination could not be performed due to pain. Other systemic examinations were unremarkable. She was provisionally diagnosed to be a case of ‘extra-pulmonary tuberculosis (on ATT continuation phase for abdominal tuberculosis), community acquired-pneumonia, urinary tract infection (UTI), sepsis and septic shock, with high suspicion of HIV due to oral thrush and emaciation’.
At the time of admission, total leucocyte count, red cell count and platelet counts were all within normal limits. Haemoglobin and mean corpuscular haemoglobin were decreased, with microchromic hypochromic anaemia, suggestive of anaemia of chronic disease. The peripheral blood smear showed few activated lymphocytes, while the liver and kidney function tests were slightly deranged.
Patient tested serologically positive for HIV-1 on day 2 of hospitalisation, negative for hepatitis viruses B and C by serology, and RT-PCR for COVID-19 was negative. Since CT was available in our tertiary care setting, it was prescribed over X-ray due to the patient’s condition. CT scan revealed a thick walled cavitary lesion in the right upper lobe, multiple bilateral reticular opacities and multiple bilateral centrilobular nodules consistent with Pneumocyctis jiroveci pneumonia (PCP). Collectively these findings were suggestive of active infective aetiology in the background of chronic infection.
A self-voided, clean catch midstream urine sample was received in microbiology department for aerobic culture and sensitivity on day 5 of hospitalisation. On routine microscopy of uncentrifuged urine, 4–5 pus cells per high power field, occasional epithelial cells and bacteria were seen. After 24 hours of aerobic incubation on Cystine-Lactose-Electrolyte-Deficient (CLED) agar at 37°C in ambient air, there was significant microbial growth (≥105 colony forming units/mL) of non-lactose fermenting colonies that appeared as gram-negative bacilli on gram staining. The isolate was oxidase positive, catalase positive and non-motile. It was identified as A. salmonicida with 98% probability and excellent identification confidence using GNID card in Vitek 2 automated identification system (bioMérieux SA, France). Further, using the N-281 card, the isolate was found susceptible to ceftazidime, amikacin, gentamicin, ciprofloxacin, levofloxacin and resistant to piperacillin-tazobactam, doripenem, imipenem, meropenem, trimethoprim-sulfamethoxazole.
Patient was admitted to the general medicine ward and prescribed intravenous fluids, antipyretic, intravenous fluconazole and intravenous cotrimoxazole along with empiric corticosteroids for septic shock. Antituberculosis treatment was continued, and high protein diet was advised. The patient continued to be in shock and was on inotropes till day 9.
After receipt of the urine microscopy and culture report, intravenous amikacin was added to the patient’s treatment regimen on day 9 of hospitalisation to cover A. salmonicida. Patient improved over the next few days, with no new complaints and inotropes were withdrawn. Patient’s blood culture as well as repeat urine culture became sterile after 3 days of targeted antibiotic therapy.
On day 13 of hospitalisation, patient displayed some abnormal behaviour, for which psychiatric consultation was sought. She was diagnosed with critical care psychosis, and treated with sertraline and clonazepam.
Outcome and follow-up
After 20 days of hospitalisation, patient was discharged with referral to antiretroviral therapy (ART) centre and advice for follow-up consultation with general medicine as well as psychiatry. The slight derangements in kidney and liver function tests were attributed to the ongoing chronic illness and did not warrant any specific intervention, anticipating becoming better with clinical improvement.
At a telephonic follow-up after 2 months, patient reported that she was taking ART as well as antitubercular therapy (ATT) and doing well. A physical follow-up was conducted at 4 months. Patient was doing fine and on ART with tenofovir-lamivudine-dolutegravir single pill and cotrimoxazole prophylaxis therapy (CPT).
This case report brings forth the need for every patient with extrapulmonary tuberculosis to be tested for HIV during initial workup itself, even though HIV burden is gradually declining. This will help in choosing diagnostic tests and their interpretation, should there be an unusual or opportunistic pathogen, and facilitate patient’s treatment accordingly.
We believe that A. salmonicida was responsible for causing UTI in this case instead of being a coloniser for more than one reasons viz, (a) A. salmonicida has never been isolated from any of the samples in our laboratory, thus ruling out its presence in the environment, (b) the urine microscopy findings, viz presence of pus cells, were indicative of urinary tract pathology. In case of extraneous contamination/colonisation pus cells would not have been present in urine, (c) A. salmonicida was isolated from urine sample before initiation of Amikacin on day 9, with significant counts (105 cfu/mL) whereas in case of colonisation the bacterial counts are usually <103 cfu/mL, and in case of insignificant bacteriuria the gram negative bacterial counts are between 103 and 105 cfu/mL, (d) the urine culture became sterile after 3 days of targeted antibiotic therapy and (e) patient became afebrile and inotropes were withdrawn, pointing towards favourable clinical response derived from amikacin induced clearance of A. salmonicida. Further, this was certainly not a case of genitourinary tuberculosis because patient presented with UTI despite being on ATT for preceding 2 months and sterile pyuria is typical finding in genitourinary tuberculosis. But in this patient A. salmonicida was isolated from the urine sample with significant count (105 cfu/mL), which resolved after 3 days of amikacin therapy with very evident clinical improvement, which would not have been possible, if the aetiology of UTI was Mycobacterium tuberculosis.
A. salmonicida has been reported to cause bacteraemia, endocarditis, ophthalmic infections and acute febrile illness in immunocompromised, as well as immunocompetent persons, usually with good clinical recovery, as summarised in table 1. To the best of our knowledge, this is only the third report of A. salmonicida infection from India, and the first report of isolation from urine globally.
The most important risk factor associated with A. salmonicida infections appears to be exposure to a contaminated water source, either through drinking water or consumption of fish.4–8 However, in our case no such history could be elicited. Thus, the source of the infection remains unknown.
The recent enhanced isolation of this organism may be attributed to increased availability of automated identification systems, along with increased awareness about rare organisms, especially in immunocompromised cases.
Aeromonas salmonicida is a rare but emerging human pathogen causing varied manifestations.
Though it is said to be found in aquatic habitat and infects patients with or without pre-existing conditions, it is not always possible to trace the source.
Isolation of bacteria in significant counts with associated findings like presence of inflammatory cells in the sample should arouse clinical suspicion and be taken as indication of the organism being true pathogen and be treated accordingly in absence of other definitive aetiology. This shall be one of those situations where trial antibiotic therapy can be life-saving and clinical response from trial antibiotic provides more corroborating evidence for the unusual organism to be actually pathogenic.
Identification of such pathogens may not be possible with conventional techniques; thus, automated systems are better.
Timely treatment of A. salmonicida results in good patient outcome.
Patient consent for publication
Contributors LL was involved in microbiological diagnosis, preparation of the draft and literature review. RB was involved in patient care and follow-up along with preparation of draft. SK supervised overall patient care. SP supervised microbiological diagnosis, conceptualised the case report, finalised the draft and is responsible for the overall content as guarantor. All authors approved the final version of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.