Thread by @Loretta_Torrago

This study by @TracyBethHoeg, @KrugAlli et al. reinvents the need for the adage "absence of evidence isn't evidence of absence" as a response to the authors’ novel approach “If you don’t have symptoms, you don’t have cases."🧵
bjsm.bmj.com/content/bjspor…

The study is allegedly about player-to-player transmission being contained by the protocols for youth ice hockey the authors develop. Alarm bells ring almost immediately when the authors introduce us to the study’s crew: a “volunteer epidemiologist”,

and other “neutral” parties.

After describing previous protocols, the authors take us to their “New Protocols” both of which can be seen in this table. With New Protocols in place, practices resume; notably without knowing the starting infection rate.
h/t @justthefacts85

Nonetheless, 148 hockey players have 500 practices over an 18 week period during which time 5 cases (down from 14) are detected.

Lest we think the volunteer epidemiologist isnt up to the task, we are told s/he has a whiteboard.

Such impressive equipment, however, can not overcome the study’s considerable methodological flaws; foremost of which is that the study is based on symptoms which the authors characterize, for reporting purposes, as “the common cold”.

By design then, the study excludes asymptomatic infections which is an odd choice for a study on the very people, the young, that the virus infects primarily asymptomatically. What’s more, even asymptomatics contribute to viral load.

This matters especially for hockey rinks where the relative frequency of outbreaks is partially attributed to the plexiglass surrounding the rink which inhibits free airflow.
washingtonpost.com/health/2020/12…

The odd nonchalance towards asymptomatic infection is made even odder when the authors describe how the one time free on-site clinic discovered “three additional asymptomatic infections.”

The study’s focus on symptoms is not the only methodological hurdle it faces. It also relies on voluntary reporting which curiously, goes to the ice hockey director first and then the epidemiologist.

Though the sentence which begins “When a family reported a positive case or potential exposure…..” excludes symptoms, this seems to be an oversight.

Given the local health department was “overwhelmed” at the time, it’s not clear the extent to which families were notified of potential exposures. More importantly, outside of the single on-site event, testing was voluntary and the burdens of testing fell to families.

This isn’t just a problem of inconvenience. The study admits parents were having to deal with insurance and/or out-of-pocket test costs.

Apparently aware of these significant hurdles, the authors admit there were likely “undetected cases”. To compensate, a survey (presumably symptom based) is conducted. There is no indication that the authors felt compelled to consider asymptomatic infection an “undetected case”.

Additionally, though it is probably a fair assumption, the possibility of post-vaxx infection or re-infection seems to be excluded in the calculation of undetected cases.

In what is arguably quite the understatement, the authors admit that they might have missed player-to-player transmission, which is an odd concession given the author's purpose is to study transmission.

However, they say “case investigations” found only “household transmission”. W/out casting doubt on the volunteer epidemiologist's efforts, tracing is difficult & not clearly possible when the only clues it follows are reported symptoms & whatever tests parents seek out & report

For example, after a positive case, the authors tell us only that “no further symptoms or postives tests were reported” but do not tell us how many of the exposed were tested.

The authors’ justification for concentrating on symptomatic cases only is because, they tell us, the risk of transmission from asymptomatic cases is just 0.7% .

Notably, that’s a *household* transmission rate which again matters very much given the object of concern is a ripe-for-transmission hockey rink. It’s not just the plexiglass either.

The authors have an additional study they say establishes asymptomatic transmission’s low risk but at this point one has to ask: If you think the asymptomatic rate is well-established, what is the point of a study of transmission in a largely asymptomatic population?