We are all fundamentally flawed as humans. We just have to do the best we can given our limitations.
I attended an interesting clinical Grand Round at my local hospital last week. Whilst the case presented was intriguing, it was the presenters’ focus on the different types of cognitive bias which are seen in clinical medicine which really caught my attention.
It got me thinking… Do the same types of bias apply when reading and interpreting microbial cultures on agar plates?
The answer is of course yes.
Below are examples of the main types of cognitive bias one might be subject to when reading agar plates:
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Confirmation Bias – Scientists may interpret bacterial growth in a way that confirms their expectations or prior hypotheses. For example, if they expect a certain antibiotic to inhibit growth, they might unconsciously downplay colonies that appear resistant.
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Anchoring Bias – The first observation or previous experience can heavily influence interpretation. If a scientist has seen a particular growth pattern before, such as satellitism of Haemophilus influenzae around Staphylococcus aureus they might assume it’s the same species or reaction without fully considering other possibilities.
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Availability Heuristic – The tendency to rely on readily available examples in memory. If a scientist recently encountered an unusual bacterial isolate, they might overestimate its likelihood when analysing new plates, leading to misidentification.
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Observer-Expectancy Effect – The scientist’s expectations may subtly influence how they interpret ambiguous results. For instance, if they believe a sample contains Streptococcus pneumoniae, they might unconsciously interpret the MALDI-TOF result as such, and ignore the possibility of Streptococcus mitis.
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Hindsight Bias – After identifying bacterial species via additional testing, e.g. MALDI-TOF, scientists might believe the identification was more obvious than it actually was when first observing the plate, leading to overconfidence in future interpretations.
…and then of course there is the classical clinical judgement bias, that of “Premature Closure” where an “easy” or quick diagnosis is made, and further investigations into a more challenging/important secondary diagnosis are withheld because of this. It happens not infrequently in clinical medicine. An example of this in the microbiology laboratory might be a patient with crystals in a synovial fluid sample leading to a diagnosis of gout, where sufficient duration of culture was not performed to pick up the secondary diagnosis of septic arthritis!
Now that we can simply google the key biochemical reactions of E. coli, maybe cognitive bias is the sort of thing we should be teaching microbiology students, so that they are aware of the sub-conscious ways we can slip up when reading agar plates, no matter how good our intentions… A nice exam question perhaps!
Michael
Unfortunately, I am aware of some colleagues that have the Weekend Bias. The plates are getting VIP fast-track service on Saturdays and Sundays—less staff, less colonies tested, less additional testing. Efficiency or weekend shift overload? We may never know!
Interesting perspective, but one would need objective data to back up your claim and whether it affected the final results. I am not aware of this issue in my own lab.
Thanks, Michael
Hi Michael
Good points. From my perspective, MLSs generally follow established guidelines, partly because they complain they have not got time to follow leads. I was part of one of the leading world teams to research M. catarrhalis, and we had some highly rated papers. This happened to me a few times in the lab, and I still deal with the phenomenon of emerging bacterial pathogens. These organisms are as easily detected in NZ as in any place on the globe. I asked an MLS in a lab I had worked in recently what was happening with antimicrobial resistance. (because I still have a -80c freezer full of isolates from the last 20 years) i suggested it would be interesing to get a BMLS student to update the family tree using our old isolates and the new ones. “We don’t have the time for research” was the answer. I have no idea what is passing over the bench now, but I would bet that emerging pathogens are missed. Emerging pathogens do not appear on MaldiTOF, nor in conventional commercial media. There is less dialogue between the MLS and the clinician than ever, so the reality of the patient journey is not known. I used to have the slogan “The role of the laboratory is to help the doctor to help the patient” (as a bilateral relationship) Competition between labs, and the policy to “test less” are also factors that limit that crucial exchange. There is also the issue of dogma, which you allude to. “It is difficult for experts to prove themselves wrong” is also a problem, and is magnified in a period where everyone wants to take the easy way (and not make waves) . This also happens when automated instruments are employed. I had the first Vitek in NZ, and it lifted our antibiotic skills, but we still questioned the results if they were not credible. My personal issue now is the use of the MGIT tubes, where a recent publication showed that 70% of NTM were missed using the MGIT. (I would say it was probably more than that) Anyway, I greatly enjoyed your article! Cheers John
PS the late Franklin Koonze used to say “no one was ever cured by exquisitely accurate taxonomy”. This is particulary true in the case of the great imitators of the 21st century, emerging bacterial pathogens
Thanks for your comments John, much appreciated!
Michael