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\begin{document}
\title{A pediatric pulmonologist's cumulative risk of acquiring Covid-19 in
outpatient practice}
\author[1]{Julian Allen}%
\author[2]{Tryce Scully}%
\affil[1]{CHOP}%
\affil[2]{The Children's Hospital of Philadelphia}%
\vspace{-1em}
\date{\today}
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\begin{abstract}
Pediatric pulmonologists, and, indeed, general pediatricians, are
exposed to the causative virus of Covid-19 , SARS-CoV2, in their daily
outpatient practices from both symptomatic and asymptomatic patients.
This risk naturally increases with multiple exposures over time. We have
developed a simple equation to calculate the probability of a
practitioner remaining Covid free over a specified time interval, given
the local population prevalence of virus, the transmissibility of the
organism or ``attack rate,'' the mitigating effects of personal
protective equipment (PPE), and the number of patients seen over the
time interval. The equation can be used to construct a Kaplan Meier
-like plot for remaining Covid free. Since studies of transmission of
SARS-CoV2 suggest a spectrum between droplet and aerosol spread, even in
asymptomatic patients and absence of aerosol generating procedures, the
type of masks protection worn by medical practitioners may mitigate risk
to different degrees. Eye protection may mitigate the risk further.
While the risk of acquiring Covid-19 in a year of practice is low, it is
not negligible. However it can be minimized. These considerations may be
helpful in deciding local risk to the practitioner according to practice
volume and in choosing the level of PPE that would result in minimizing
that risk.%
\end{abstract}%
\sloppy
TITLE: A pediatric pulmonologist's cumulative risk of acquiring Covid-19
in outpatient practice
Julian Allen, M.D. and Tryce Scully, M.S.
Corresponding Author:
Julian Allen, M.D.
Professor of Pediatrics
Perelman School of Medicine at the University of Pennsylvania
Pulmonary Division
Colkett 11\textsuperscript{th} floor
The Children's Hospital of Philadelphia
3401 Civic Ctr. Blvd
Philadelphia, PA 19104
Email: allenj@email.chop.edu
Key Words: Covid-19, risk, N95 mask, surgical mask, infectious disease
transmission
Running Title: Cumulative risk of acquiring Covid-19
A pediatric pulmonologist's cumulative risk of acquiring Covid-19 in
outpatient practice
To the Editor:
Pediatric pulmonologists, and, indeed, general pediatricians, are
exposed to the causative virus of Covid-19 , SARS-CoV2, in their daily
outpatient practices from both symptomatic and asymptomatic patients.
This risk naturally increases with multiple exposures over time. To
describe how risk could be affected by disease prevalence,
transmissibility, patient volume, and personal protective equipment
(PPE), we have developed a simple equation for the probability of a
practitioner remaining Covid free over a specified time interval. We
were unable to find similar calculations in the literature, although
analogous concepts have been explored in considering communicable
disease risk to \emph{patients} from multiple exposures to practitioners
and other patients in healthcare settings (1).
In our analysis, we assume that R, the risk of each patient encounter=
average prevalence in population (P) x transmission rate/encounter (T) x
PPE mitigation factor (M).
If 1-R = probability of remaining Covid- free after one encounter, and
total encounters (E) over one year = encounters/day x patient days/week
x weeks/year, then to calculate \textbf{Cumulative Covid-free}
probability \textbf{(CFPc)} :
CFPc = (1-R)\textsuperscript{E}
CFPc = (1-PTM)\textsuperscript{E}
For example, if one makes the following assumptions for the clinical
practice of one practitioner over a year:
Daily population prevalence (P) of 2\% over the exposure period = 0.02
(2)
Transmission rate (T) of 1 in every 100 close encounters = 0.01 (3)
PPE mitigation factor (M) = 1.0 for no mask, 0.33 for a surgical mask,
and 0.04 for an N95 mask (4)
Encounters/year (E) = 12 patients seen/day x 3 Patient days/week x 46
Patient Weeks/year = 1656
then, the probability of remaining Covid free for a year if the
practitioner wears a surgical mask can be calculated as
CFPc = (1 -- 0.02x0.01x0.33)\textsuperscript{1656} =
0.99993\textsuperscript{1656} = 0.89, or 89\%.
Similarly, the probability is 72\% with no mask, and 98\% with an N95
mask. The equation can be used to construct a Kaplan Meier -like plot
for remaining Covid free (Figure)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}
\end{center}
\end{figure}
Studies of transmission of SARS-CoV2 suggest a spectrum between droplet
and aerosol spread, even in asymptomatic patients and absence of aerosol
generating procedures (5). Thus the type of masks worn by medical
practitioners may mitigate risk to different degrees. Our equation is
modifiable, according to local prevalence, transmission efficiency,
number of patients seen per year by the provider, and quality of mask
mitigation. Eyewear may further mitigate this risk (4). The figure shows
that while the risk of acquiring Covid-19 in a year of practice is low,
it is not negligible. However it can be minimized. These considerations
may be helpful in deciding local risk to the practitioner according to
practice volume and in choosing the level of PPE that would result in
minimizing that risk.
Julian Allen, MD
Tryce Scully, MS
The Children's Hospital of Philadelphia
References
\begin{enumerate}
\tightlist
\item
Payet C, Voirin N, Vanhems P, Ecochard R. A statistical model to
assess the risk of communicable diseases associated with multiple
exposures in healthcare settings. BMC Medical Research methodology
2013;13:26. (http:www.biomedcentral.com/1471-2288/13/26)
\item
Goldfarb IT, Diouf K, Barth WH, Robinson JN, Katz D, Gregory KE,
Ciaranello A, Yawetz S, Shenoy ES and Klompas M. Universal SARS-CoV-2
testing on admission to the labor and delivery unit: Low prevalence
among asymptomatic obstetric patients. Infection Control \& Hospital
Epidemiology 2020; (1--2 doi:10.1017/ice.2020)
\item
Huang Y-T, Tu Y-K and Lai P-C. Estimation of the secondary attack rate
of COVID-19 using proportional meta-analysis of nationwide contact
tracing data in Taiwan. Journal of Microbiology, Immunology and
Infection 2020;
(https://doi.org/10.1016/j.jmii.2020.06.003https://doi.org/10.1016/j.jmii.2020.06.0031684-1182)
\item
Chu DK, Akl EA, Duda S, Solo K, Yaacoub S, Schu\selectlanguage{english}nemann HJ, on behalf of
the COVID-19 Systematic Urgent Review Group Effort (SURGE) study
authors Physical distancing, face masks, and eye protection to prevent
person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic
review and meta-analysis. The Lancet 2020; (www.thelancet.com 2020;
https://doi.org/10.1016/S0140-6736(20)31142-9)
\item
Morawska L,~~Milton DK. It is Time to Address Airborne Transmission of
COVID-19. Clinical Infectious Diseases\emph{,} 2020;
(~https://doi.org/10.1093/cid/ciaa939)
\end{enumerate}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Covid-Free-Probability-KM-TIFF/Covid-Free-Probability-KM-TIFF}
\end{center}
\end{figure}
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