Case of the Month

August 2010

A previously healthy 27 year old man sustained a high spinal cord injury whilst diving into shallow water in a river in the Western Cape in late summer. He was found floating on the surface of the water after an unspecified time period, and taken to hospital. He required intubation and ventilation for respiratory support. Three days later he was transferred to a nearby tertiary hospital for specialist spinal surgery.

On arrival the patient appeared stable. However, about 24 hours later he deteriorated suddenly, becoming hypotensive, with respiratory distress, hypoxia and decreased level of consciousness. A pulmonary embolus was suspected. Despite resuscitation, his condition deteriorated and he died 24 hours later.

Laboratory results available about 12 hours after his sudden deterioration showed that his white cell count had risen sharply, from 4.1 x 109 /L the previous day, to 24 x 109/L. A blood culture taken at the time grew Gram-negative bacilli after 6 hours and the patient was started on ertapenem. Chest x-ray reported new, extensive bilateral changes.

Following his demise, the blood culture isolate was identified as Aeromonas hydrophilia, resistant to ampicillin and co-amoxiclav, but susceptible to cephalosporins, carbapenems, ciprofloxacin and aminoglycosides.

A tracheal aspirate taken 8 hours prior to his rapid deterioration showed 3+ WBCs on microscopy and cultured a scanty growth of Klebsiella pneumoniae, resistant to ampicillin only, as well as a scanty growth of a fully sensitive Haemophilus influenzae.

A second blood culture taken 20 hrs after starting ertapenem was negative. A forensic post-mortem confirmed the presence of bilateral pneumonia with associated pleuritis and small pleural effusions.

Question 1: What organisms are associated with infection in near drowning incidents?

Answer to Q1

As near drowning incidents occur mostly in young healthy males, one would expect a good recovery rate for associated pneumonia. However, case fatality rates of up to 60% have been reported, although the attributable mortality is unknown.

A variety of organisms have been associated with pneumonia following near drowning incidents, including:

  • Aeromonas species
  • Legionella species
  • Burkholderia pseudomallei (in endemic areas)
  • Chromobacterium violaceum
  • Francisella philomiragia & other Enterobacteriaceae
  • Endogenous organisms from the oropharyngeal flora, e.g. Streptococcus pneumoniae

Whilst 'exotic' organisms predominate, it is possible that the association of other more common organisms such as Pseudomonas aeruginosa remains unrecognised due to under-reporting of such infections in contrast to the rarer microorganisms.

Vibrio species, while commonly found in aquatic environments, typically result in soft tissue infections or bacteremia, rather than pneumonia.

While a number of opportunistic fungi are present in water, Pseudallescheria boydii and Aspergillus species are most commonly described as causing pneumonia in immunocompetent hosts. P. boydii may cause a delayed presentation of disseminated disease, typically involving the central nervous system.

Question 2: What is your interpretation of the pathogens grown on tracheal aspirate? Would you give empiric antimicrobials to patients with near drowning?

Answer to Q2

The two organisms isolated in small amounts from the tracheal aspirate could represent normal respiratory flora, and/or colonisation. The diagnosis of pneumonia following near drowning can be extremely difficult, and is based on clinical evidence of pneumonia and microbiological evidence of infection. Isolates obtained from blood culture are particularly informative.

A low threshold for starting empiric antibiotics is advised, to avoid potential serious consequences. Suggested antibiotic options include:

  • beta-lactam / beta-lactamase inhibitor combination with an aminoglycoside in severe infections,
  • Ciprofloxacin plus clindamycin, or alternatively, a respiratory fluoroquinolone e.g. moxifloxacin. This option should be used in cases of penicillin allergy

Prophylactic antibiotics are not generally recommended in near drowning incidents, although they may be considered in the setting of severe aspiration or exposure to contaminated water.

Question 3: What are the microbiological characteristics of Aeromonas hydrophilia?

Answer to Q3

Aeromonas are facultatively anaerobic, non-spore forming Gram-negative bacilli. Previously included in the Vibrionaceae family they are now classified as a separate family, with up to 24 species. However, not all species are fully accepted, and various controversies complicate the detailed taxonomy of Aeromonas. Most human infections are due to 3 species, namely A. hydrophilia sensu stricto, A. caviae and A. veronii bv. sobria.

Aeromonas species are ubiquitous in the environment, particularly associated with water, e.g. rivers, dams, ponds, and may be found in low concentrations in food.

They are also associated with outbreaks of disease in fish and amphibians, for example, red leg disease in frogs, and cause infections in insects and vertebrates. Human infections most commonly result from environmental or zoonotic exposure, for example, leeches used for medicinal purposes and snake bites may transmit Aeromonas spp.

In the laboratory:

  • Aeromonas spp. grow easily on non-selective media, with more than 90% showing beta-haemolysis on sheep blood agar.
  • They also grow on most selective enteric media.
  • Laboratory identification of Aeromonas, at least to the complex level, is relatively simple, based on standard biochemical tests, including oxidase (Aeromonas test oxidase positive).
  • Commercial identification systems, such as Vitek, may have difficulties in speciation.
  • Specialised media are available to facilitate identification from stool specimens. Despite its uncertain significance as a cause of gastro-enteritis, it is advisable to report the presence of Aeromonas in the stool to clinicians, provided it is present as a pure culture or in significant numbers

Although the use of different methods for determining MIC values, including Etest® appears to be acceptable for most antibiotics, CLSI guidelines have been recently introduced for antimicrobial susceptibility testing which will facilitate disk diffusion testing for Aeromonas. One caution is that current knowledge of susceptibility patterns is based mainly on the 3 predominant human pathogens mentioned previously.

Question 4: Discuss the clinical manifestations and treatment of Aeromonas hydrophilia infection

Answer to Q4

Aeromonas species cause a wide spectrum of clinical disease, commonest being gastroenteritis, bloodstream and soft tissue infections.

  • Gastroenteritis: There is still uncertainty as to whether Aeromonas is a true enteropathogen, as animal models are lacking and volunteer studies have failed to reproduce infection. However, Aeromonas is not present in normal gut flora. Aeromonas gastroenteritis occurs worldwide, affecting predominantly healthy persons of all ages, particularly in summer months (at least in temperate climates). The diarrhea which is usually acute, may vary in severity from mild to severe, and may be watery or bloody in nature.
  • Bloodstream infections occur more commonly, though not exclusively in immunocompromised hosts such as those with liver cirrhosis or haematological malignancies.
  • Skin and soft tissue infections (SSTIs) are typically community acquired infections related to trauma and contamination with water or soil. While of varying severity, they tend to be rapid in onset and may be fairly aggressive, resulting in necrotizing fasciitis and myonecrosis in some cases. Aeromonas spp. were the commonest pathogens causing SSTIs in survivors of the 2004 East Asian tsunami. In our local experience the most common source of Aeromonas isolates is SSTI, including burns.
  • Intra-abdominal infection, such as spontaneous bacterial peritonitis can occur; Aeromonas is the 3rd commonest cause of this condition in Southeast Asia.
  • There is an increasing number of reported cases of respiratory tract infection, particularly pneumonia, a proportion of which follow near drowning incidents. Infection may progress rapidly within hours with a mortality rate of up to 50%.

Aeromonas, spp. are almost universally susceptible to fluoroquinolones which are probably the antibiotic of choice. Choice of beta-lactam antibiotics is complicated by the fact that most Aeromonas spp. possess chromosomal ampC type beta-lactamases (resulting in resistance to coamoxiclav and first to third generation cephalosporins), while a chromosomal metallo-betalactamase, CphA (conferring resistance to carbapenems) is also widely distributed.


  1. Ender PT, Dolan MJ. Pneumonia associated with near-drowning. Clin.Infect.Dis. 1997 Oct;25(4):896-907.
  2. Janda JM, Abbott SL. The genus Aeromonas: taxonomy, pathogenicity, and infection. Clin. Microbiol. Rev. 2010 Jan;23(1):35-73.
  3. Katragkow A, Dotis J, Kotsiou M, Tamiolake M, Roilides E. Scedosporium apiospernum infection after near-drowning. Mycoses 2007 Sep;50(5):412-421.
  4. Miyake M, Iga K, Izumi C, Miyagawa A, Kobashi Y, Konishi T. Rapidly progressive pneumonia due to Aeromonas hydrophila shortly after near-drowning. Intern. Med. 2000 Dec;39(12):1128-1130.
  5. Skoll PJ, Hudson DA, Simpson JA. Aeromonas hydrophila in burn patients. Burns 1998 Jun;24(4):350-353.
Lesson learnt

While prophylactic antibiotics are not generally advised, near-drowning patients can experience very rapid onset of severe respiratory symptoms due to pneumonia. Diagnosis of pneumonia can be difficult and positive blood cultures can be extremely helpful. Aeromonas species are classic pathogens associated with pneumonia following near drowning.

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