In May 2018, Paul Cahill settled a medical malpractice claim against a medical laboratory on behalf of a 46-year-old woman who suffered progressive spinal damage from inadequately treated tuberculosis. The patient had been diagnosed with tuberculosis. The standard treatment for tuberculosis requires a combination of antibiotic drugs selected on the basis of the patient’s specific strain and its pattern of drug sensitivities and drug resistances. The laboratory responsible for testing the patient’s tuberculosis isolate failed to perform the susceptibility testing properly. The antibiotic regimen that followed did not adequately suppress the patient’s specific strain of Mycobacterium tuberculosis. The infection progressed. It localized in the spine. By the time it was identified, the patient had developed progressive vertebral collapse with nerve root compression, neurogenic claudication, and sciatica. She required an extensive reconstructive spinal procedure including a multi-level laminectomy, a discectomy, an L4 osteotomy, an epidural decompression of the affected nerve roots, and a spinal fusion with pedicle screws and bone graft.
Laboratory error in tuberculosis testing is a recognized category of medical negligence claim. It is doctrinally distinct from physician error in tuberculosis treatment because the breach occurs in a setting that has its own well-defined standards of practice, its own accreditation framework, and its own quality control infrastructure. In Ontario, the regulatory system for medical laboratories is detailed and longstanding, and the standard of care for tuberculosis susceptibility testing in particular is described in detail in the published microbiology literature and in the protocols of the relevant accrediting bodies. The errors that can arise in this kind of testing are well-characterized and well-known.
The civil claim was advanced against the medical laboratory. The settlement was reached without admission of liability and the terms are confidential. The clinical and legal pattern, however, is one that bears explaining, both because tuberculosis remains a present concern in Ontario and because laboratory error is an underdiscussed category of medical malpractice.
The clinical context
Tuberculosis is a chronic infectious disease caused by Mycobacterium tuberculosis. The bacterium is transmitted by airborne droplets and most commonly causes pulmonary disease, but extrapulmonary involvement is reported in approximately 15 to 20 percent of cases and can affect almost any organ system. Skeletal tuberculosis accounts for a small but clinically significant fraction of extrapulmonary disease. Within skeletal tuberculosis, the spine is by far the most common site of involvement. Spinal tuberculosis is also known as Pott’s disease, named for the eighteenth-century British surgeon who first described the condition.
Spinal tuberculosis affects the vertebral bodies preferentially over the intervertebral discs. The infection produces a slow, insidious destruction of the bone. The vertebral body weakens. Eventually it collapses. As one vertebra collapses, the spine loses its normal alignment and develops a forward-angled deformity known as kyphosis. The collapsed bone can compress the nerve roots that exit the spinal canal at that level, producing radicular pain, weakness, and sensory disturbance in the body parts those nerves supply. Where the collapse is sufficient to compress the spinal cord itself, the patient can develop paraparesis, paraplegia, or, in cervical involvement, quadriparesis. The thoracic and thoracolumbar spine are the most common sites of disease, but lumbar involvement is also reported.
The treatment of tuberculosis, including spinal tuberculosis, is principally pharmacological. The standard regimen consists of combination antibiotic therapy continued over a prolonged course, with the specific drugs selected on the basis of the patient’s strain and its drug-susceptibility profile. The four traditional first-line drugs are isoniazid, rifampin (also written as rifampicin), ethambutol, and pyrazinamide, often referred to by the acronym RIPE. The initial intensive phase typically uses all four drugs for two months; the continuation phase typically uses two of the drugs (isoniazid and rifampin) for an additional four to seven months, for a total course of six to twelve months depending on the site of disease and the patient’s clinical response. Spinal tuberculosis is generally treated for at least nine months, and often longer, because of the difficulty of penetrating antibiotic into the avascular core of an infected vertebra.
Surgical intervention is reserved for specific indications: progressive neurological deficit, spinal instability or significant deformity, intractable pain, large abscess collections, and treatment-resistant disease. The surgery, when it is required, is among the more complex procedures in modern orthopedic and neurosurgical practice. The objectives are decompression of compressed neural structures, debridement of infected tissue, correction of deformity where possible, and stabilization through fusion of the involved spinal segments.
The role of drug susceptibility testing
The pharmacological treatment of tuberculosis depends critically on knowing which drugs the patient’s specific strain is susceptible to. The reasons are interrelated.
First, drug-resistant tuberculosis is a present clinical reality. Resistance to isoniazid alone is the most common form. Resistance to both isoniazid and rifampin defines multidrug-resistant tuberculosis (MDR-TB). Extensively drug-resistant tuberculosis (XDR-TB), which adds resistance to fluoroquinolones and to at least one of the injectable second-line drugs, is rarer but increasing. A patient with MDR-TB will not be adequately treated by the standard RIPE regimen; the disease will progress despite apparent compliance with therapy.
Second, the consequences of inadequate treatment are not confined to the lungs. As the disease progresses in a poorly suppressed state, the bacteria can disseminate hematogenously to extrapulmonary sites. The skeletal system, particularly the spine, is among the most susceptible. A patient whose tuberculosis is incompletely controlled because of an undetected resistance pattern can develop spinal involvement long after the initial infection was nominally treated.
Third, the published clinical literature is unambiguous that drug susceptibility testing should be performed at the time of initial culture confirmation, and that the treatment regimen should be adjusted on the basis of the results. The published microbiology references treat phenotypic susceptibility testing in liquid culture systems such as the BACTEC MGIT 960, performed against at least the first-line agents, as the established standard of care. Molecular nucleic acid amplification tests for resistance markers have supplemented but not replaced traditional culture-based testing. The institutional infrastructure to perform this testing has been in place in Ontario reference laboratories for decades.
The laboratory process by which susceptibility testing is performed has three phases, each of which can produce errors: a pre-analytical phase (specimen collection, transport, accessioning), an analytical phase (the actual testing), and a post-analytical phase (results interpretation, reporting, and communication to the treating clinician). Ontario regulatory analysis of laboratory errors has identified that the majority of errors occur in the pre-analytical and post-analytical phases rather than in the analytical phase itself.
The patient and the gap in testing
The patient was 46 years old. She had been diagnosed with tuberculosis and was being treated. The laboratory responsible for testing her Mycobacterium tuberculosis isolate failed to properly test for susceptibilities. The specific nature of the laboratory’s failure is not detailed in the public description and is appropriately kept confidential; the recognized failure modes in this category of case include failure to perform the testing at all, performance of the testing using inappropriate methods, errors in the analytical process producing falsely susceptible results, failure to report all of the tested drugs, and failure to communicate the results to the treating physician in a timely or actionable way.
The consequence was the same regardless of which failure mode produced it. The patient’s tuberculosis was treated with an antibiotic regimen that did not adequately suppress her specific strain. The infection progressed. It localized in the spine. The vertebral bodies were progressively destroyed. The bone collapsed. The nerve roots exiting the spinal canal at the affected levels were compressed by the collapsed bone and by the surrounding inflammatory tissue. The patient developed the clinical syndrome of nerve root compression: pain radiating in the distribution of the affected nerve, weakness in the muscles those nerves supply, and altered sensation in the corresponding skin territory. She developed neurogenic claudication, a pattern of leg pain that comes on with standing or walking and resolves with sitting or forward flexion, caused by mechanical or vascular compromise of the spinal nerves. She developed sciatica, the lay term for irritation of the sciatic nerve or its component roots.
By the time the spinal involvement was identified and addressed, the structural damage was significant enough that surgical reconstruction was required. The procedure included a multi-level laminectomy, removing the posterior bony arches of the affected vertebrae to relieve the pressure on the underlying neural structures. It included a discectomy, removing damaged intervertebral disc material. It included an L4 osteotomy, a controlled bone cut at the L4 vertebra to allow correction of the spinal alignment. It included an epidural decompression of granulation tissue (the inflammatory scar tissue produced by chronic infection) that was compressing the nerve roots. It included a spinal fusion with pedicle screws and bone graft, joining the affected vertebrae into a single rigid unit to restore spinal stability and prevent further deformity.
Each of these procedures, taken on its own, is a significant operation. Together, they represent a substantial reconstructive intervention for a patient whose spine had been compromised by infection that should have been controllable with appropriate antibiotic therapy.
The legal framework
A laboratory negligence claim sits within the broader category of medical malpractice but has its own analytical structure. The general elements of a civil malpractice claim are explained in our foundational post on suing for medical malpractice in Ontario. Their application to a case of laboratory failure is as follows.
Standard of care. The standard of care for a medical laboratory performing tuberculosis susceptibility testing is defined by accreditation standards, regulatory requirements, and the published microbiology literature. In Ontario, medical laboratories are regulated under the Laboratory and Specimen Collection Centre Licensing Act and subject to the standards of the Ontario Laboratory Accreditation program. Beyond the Ontario-specific framework, medical laboratories typically operate to the standards of the Clinical and Laboratory Standards Institute and the College of American Pathologists, both of which publish detailed guidance on susceptibility testing methods, quality control, and reporting practices. The standard of care for a medical laboratory is not perfection. It is the standard of a reasonable and prudent laboratory of the same type performing the same kind of testing in the same circumstances.
For tuberculosis susceptibility testing specifically, the standard requires that susceptibility testing be performed at the time of culture confirmation, that the testing include the first-line drugs at minimum, that the testing be performed using accepted methods (such as the BACTEC MGIT 960 system or its equivalents), that the results be interpreted by appropriately qualified personnel, and that the results be communicated to the treating physician in a form that allows the treatment regimen to be adjusted. A failure at any of these steps, where the failure is not within the range of reasonable variation in laboratory practice, is a breach of the standard.
Causation. Causation in a laboratory error claim of this kind is supported by the well-established clinical relationship between drug-resistant tuberculosis, inadequate antibiotic treatment, and disease progression. Where the patient’s strain was resistant to one or more of the drugs in her standard regimen, and the laboratory’s failure caused that resistance to go undetected, the patient was effectively receiving treatment that her strain could withstand. The disease progressed because the treatment was inadequate. The progression to extrapulmonary involvement followed the natural history of inadequately treated tuberculosis. The spinal involvement, the vertebral collapse, the nerve root compression, and the need for reconstructive surgery are all recognized consequences of progressive spinal tuberculosis. Where the expert evidence supports the conclusion that proper susceptibility testing would have led to an effective regimen, that the effective regimen would more probably than not have controlled the infection before it reached the spine, and that the patient’s outcome would have been materially better, the causal chain from breach to injury is supported.
Damages. The damages in a case of permanent spinal damage from inadequately treated tuberculosis include general damages for pain and suffering and loss of enjoyment of life, lost past and future income, the cost of past and future care including the substantial surgical and rehabilitative care the patient required, and the cost of future medical follow-up. A patient who has undergone multi-level lumbar surgery with fusion typically has lasting functional limitations, including reduced spinal flexibility, recurrent back pain, and increased risk of further spinal complications at the levels adjacent to the fusion. For a 46-year-old patient at the height of her working life, the future-income and future-care components of damages can be substantial.
Duty of care running from a laboratory. The duty of care from a medical laboratory to the patient whose specimen it tests is well-established in Canadian negligence law. The laboratory is not in a direct treatment relationship with the patient, but the patient is a foreseeable user of the laboratory’s product (the test result), and the laboratory’s conduct foreseeably affects the patient’s treatment. The duty extends to the accuracy of the testing, to the appropriate reporting of the results, and to communication of any limitations or concerns that should affect the treating physician’s reliance on the results.
How the case resolved
The matter settled on confidential terms before trial. The factors that supported a productive resolution included expert evidence on the laboratory standard of care for tuberculosis susceptibility testing, expert evidence on the causal link between the laboratory’s failure and the patient’s spinal involvement, and well-documented damages reflecting the patient’s reconstructive surgery and ongoing functional limitations.
Why this case matters
For patients receiving treatment for tuberculosis or any other infection that requires drug susceptibility testing, the lesson of this case is to ask, explicitly, whether the testing has been performed and what the results show. A patient is entitled to know which drugs her infection is susceptible to and which it is resistant to, and to know whether the antibiotic regimen she is receiving has been chosen on the basis of that information. If the answers are uncertain, a request to speak with an infectious diseases specialist is a reasonable next step.
For laboratories and the clinicians who depend on them, the lesson is that the standard of care for tuberculosis susceptibility testing is well-defined and that the courts will apply it. The methods are established, the equipment is widely available, the personnel can be trained, the quality control protocols are published, and the reporting expectations are clear. Where a laboratory fails to test, fails to test using accepted methods, fails to report all relevant drugs, or fails to communicate the results in a usable way, and the failure causes a patient to receive inadequate antibiotic therapy with resulting disease progression, the analytical structure of a malpractice claim is straightforward.
For the broader practice of medical malpractice litigation in Ontario, this case sits in the smaller but well-recognized category of claims against medical laboratories rather than against treating physicians. The doctrinal framework draws on laboratory accreditation standards, on the published microbiology literature, on regulatory analysis of laboratory error patterns, and on the principles of negligence and duty of care that apply to any defendant whose conduct foreseeably affects a patient’s outcome. The analytical structure of a laboratory negligence claim differs from that of a physician negligence claim, and the expert evidence is drawn from different sources, but the elements of the cause of action are the same.
Settlement Date: May 2018
Jurisdiction: Ontario
Counsel for the plaintiff: Paul J. Cahill
