Causal opacity

Medicine as a science is predicated on causality. We seek to understand the causes of disease. Similarly, in the field of patient safety, we aim to determine the causes of adverse outcomes: What factors led the nurse to administer the wrong dose of heparin to Mr. Smith? What caused the surgeon to operate on the wrong knee? Using root cause analysis, we can work backwards from the adverse event to determine the underlying causes. 

Now consider the case a of 24-year old man hospitalized for 3 months following multiple, life-threatening injuries following a motorcycle crash. He required 17 operative procedures, a 4-week ICU stay, and had numerous invasive devices (including central venous lines, endotracheal tube, urinary catheter, ventriculostomy catheter, arterial line, and external fixating devices). On hospital day 93, he develops MRSA bloodstream infection. The magic question is this: when was MRSA transmitted to this patient? And, of course, in cases such as this, we are never able to answer that question. The field of infection prevention is plagued by causal opacity—we are rarely, if ever, able to connect cause to outcome in non-epidemic healthcare associated infections.

In infection prevention, causal opacity is the result of two factors. First, the transmission event is silent since the pathogens are invisible to the eye. Second, the incubation period temporally separates cause from effect. With multidrug resistant organisms, the intermediate state of colonization, which can extend for very long periods of time, can separate transmission from onset of infection by months or even years.

Causal opacity also negatively impacts hand hygiene compliance. Imagine if you failed to wash your hands, examined a patient, and the infection in the patient manifested within seconds after touching the patient. Like an instantaneous electric shock, the immediate feedback would probably keep you from ever failing to wash your hands again. Recently, causal opacity has hampered our ability to understand why currently available personal protective equipment may be failing us in caring for patients with Ebola virus infection.

The end result is that causal opacity makes it harder to hold persons and systems accountable with regards to infection prevention. Yes, causal opacity sucks. But it’s an integral part of what we signed up for. Otherwise, we’d all be cardiologists or urologists—driving better cars, but bored silly.


  1. Fantastic article. What are your thoughts about the issue of causal opacity and the recent developments with Medicare reimbursements? Won't tracking back to the source of infection play a significant role in at-risk or low-performing hospitals as they work towards lower infection rates? I would imagine this is a very difficult obstacle.

  2. Lack of reimbursement by Medicare certainly raises the stakes, but for any given infection the problem of causal opacity is still present.


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