On 30 May 2018, four days post-delivery, a repair of the MMC was performed with insertion of a ventriculo-peritoneal (VP) shunt. CSF specimens were submitted for routine microbiological and biochemical analysis.

Gram-negative bacilli were observed on CSF Gram stain and on 31 May 2018, meropenem was commenced. The following day, an extensively drug resistant (XDR) Acinetobacter baumannii (A. baumannii) was isolated, only susceptible to colistin. A combination of colistin + meropenem was commenced. Patient isolation and strict contact precautions were recommended as infection prevention and control measures. A repeat CSF specimen was submitted for microbiological analysis which yielded the same organism.

A week later, a tracheal aspirate was submitted for MC&S for suspected hospital-acquired pneumonia and a colistin-resistant XDR A. baumannii was isolated. On 12 June 2018, the colistin-resistant A. baumannii was then isolated from CSF.

A few days after the CSF was submitted, the patient underwent wound debridement, washout and VP shunt removal in theatre. On 20 June 2018, an external ventricular drain (EVD) was inserted in theatre. Repeat CSF samples continued to yield XDR A. baumannii resistant to colistin. The CSF and septic marker results appear in the table below.

Investigations: CSF analysis

GNCB: Gram-negative coccobacilli
Colistin susceptibility: ≤ 2 ug/ml, minimal inhibitory concentration (CLSI,M27)

On 30 July 2018, a joint decision between clinical microbiologists and neonatologists to start intrathecal amikacin and colistin was made, taking into account the causative organism’s susceptibility profile, the poor intracranial penetration of colistin, and the reported synergy of antimicrobial agents with successful patient outcomes from anecdotal case reports. The neonate experienced seizures following intrathecal antibiotic therapy; due to concerns of possible neurotoxic side effects, the intrathecal administration of antibiotics was stopped and intravenous colistin and meropenem therapy was continued.

The neonate was extubated and subsequently moved to a step-down ward for palliative care, and a decision made not to resuscitate.

On 5 September 2018, at 68 days of life, the baby demised in the ward after having received 62 days of colistin and 63 days of meropenem.

Clinical microbiological diagnosis: Colistin-heteroresistant Acinetobacter baumannii ventriculitis in a neonate with congenital meningomyelocele and hydrocephalus

Brief discussion about the clinical problem:

Shunt infections are seen in 3% to 20% of patients undergoing ventriculo-peritoneal shunt placement. Ventricular infection from multidrug-resistant (MDR) A. baumannii is a major complication of intracranial procedures with a mortality rate of 71%.

This patient was possibly infected with both colistin susceptible and resistant sub-populations of A. baumannii (heterogeneous population) or developed colistin resistance while on therapy. Heteroresistance was not confirmed according to the current gold standard which is population analysis profiling. Heteroresistance is a term more commonly associated with S. aureus and glycopeptide susceptibility i.e. hGISA/hVISA. It is less well-described in Gram negative bacteria but has emerged as a concern in determination and interpretation of susceptibility results, especially in instances of poor clinical response and where susceptibility results are not categorically conclusive. In A. baumannii heteroresistance to colistin has been attributed to the loss of lipopolysaccharide production. The clinical significance of heteroresistance remains contentious and is difficult to discern given the varied definitions and methodology employed in determination of heteroresistance. However, there is little doubt that subpopulations of bacteria with varied susceptibility to a particular antimicrobial agent play a role in specific infections, especially where there is prolonged antimicrobial use, device-associated infections or chronic infections with source control issues. This is both a diagnostic and clinical challenge in terms of optimizing management.

Intraventricular (IVT) and intravenous (IV) colistin are used as the last resort of treatment of MDR A. baumannii ventriculitis/meningitis due to poor CSF penetration despite inflammation. Colistin-associated neurotoxicity is also a concern, occurring in up to 21.7% of these cases thereby limiting its use. There is no standardised protocol for the management of colistin resistant A. baumannii ventriculitis/meningitis. Whilst case reports offer some guidance, larger studies are needed to define optimal treatment strategies. At present, such cases require an individualised treatment approach.

Question 1 - What are the signs and symptoms of a VP shunt infection?