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\title{}



\author[1]{Fabian F. Fay }%
\author[2,3,4,5]{Carlos Arturo Alvarez-Moreno}%
\author[6]{Pablo E Bonvehi}%
\author[7]{Carolina Cucho Espinoza}%
\author[8]{Marco Luis Herrera Hidalgo}%
\author[9,10]{Marcel Marcano-Lozada}%
\author[11]{Carlos M. Perez}%
\author[12,13,14,15]{Alvaro Pulchinelli}%
\author[16]{Vinicio Klever Sáenz-Flor}%
\author[15,17]{Antonio Condino-Neto}%
\affil[1]{CIBIC Laboratories, Rosario, Argentina}%
\affil[2]{Faculty of Medicine, National University of Colombia }%
\affil[3]{Clinica Universitaria Colombia}%
\affil[4]{Clinica Colsanitas}%
\affil[5]{Bogota, Colombia}%
\affil[6]{Infectious Diseases Unit, Clinical Investigation and Medical Education Center  Buenos Aires, Argentina}%
\affil[7]{School of Medicine, National University of San Marcos, Dos de Mayo Hospital  Lima, Peru}%
\affil[8]{University of Medical Sciences  San Jose, Costa Rica}%
\affil[9]{Angios Vascular Center and Wound Clinic  Caracas, Venezuela}%
\affil[10]{Juan Pablo II University San Jose, Costa Rica}%
\affil[11]{Faculty of Medicine and Science, San Sebastian University,  Clínica Universidad de los Andes  Santiago, Chile}%
\affil[12]{Federal University of São Paulo}%
\affil[13]{Brazilian Society of Clinical Pathology}%
\affil[14]{Fleury Medicina e Saúde Laboratory }%
\affil[15]{São Paulo, Brazil}%
\affil[16]{School of Medicine, University of Equator  Quito, Ecuador}%
\affil[17]{Department of Immunology, Institute of Biomedical Sciences, University of Sao Paulo}%


\vspace{-1em}



  
  \date{June 10, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Latin America accounts for roughly one-quarter of global COVID-19 cases
and one-third of deaths. Health inequalities in the region lead to
barriers regarding the best use of diagnostic tests during the pandemic.
There is a need for a simplified guideline in the region that takes into
consideration the available health resources, international guidelines,
medical literature, and local expertise.

Nine experts from different Latin American countries developed a
simplified algorithm for COVID-19 diagnosis in the region, using a
modified Delphi method. Twenty-four questions related to diverse
diagnostic settings were initially proposed, followed by an extensive
discussion of the literature and experts' experience.

According to time from close contact or symptom onset, the algorithm
considers three different timeframes ([?]7 days, 8--13 days, and [?]14 days)
and discusses diagnostic options for each one. SARS-CoV-2 real-time
reverse transcription polymerase chain reaction (rRT-PCR) continues to
be the diagnostic test of choice from Day 1 to Day 14 after symptom
onset or close contact, although antigen testing may be used in
high-prevalence settings or in particular situations (such as from Day 0
to Days 5--7 of symptom onset). Antibody assays may be used for
diagnostic confirmation, mainly after Day 14, if there is an
epidemiological or individual need. If the clinical suspicion is very
high, but other tests are negative, these assays may be used as an
adjunct to decision-making from Days 8--13.

The proposed algorithm is intended to be used as a support for COVID-19
diagnosis decision-making in Latin America.%
\end{abstract}%



\sloppy




\section*{Introduction}

{\label{introduction}}

In May 2020, the Pan American Health Organization (PAHO) declared the
region an epicenter of the disease (Pan American Organization, 2020) and
in November 2020, cumulative COVID-19 cases in Latin America accounted
for around 24\% of all cases and 33\% of all deaths globally. (World
Health Organization, n.d.)

Although PAHO (Pan American Health Organization, 2020) and other
organizations (World Health Organization, 2020a)(2019-nCoV Working
Group. Communicable Diseases Network Australia., 2020) have released
laboratory guidance for diagnosing COVID-19 cases, few have considered
the availability of tests when making these recommendations. Latin
America is a region with great socio-economic contrasts (World Bank
Development Indicators DataBank, n.d.), as well as unequal health
resources and, like in developed countries (Pablos-M\selectlanguage{ngerman}éndez et al., 2020),
the availability of COVID-19 tests and trained personnel are not exempt
from supply chain or personnel pressures.

A panel of Latin American experts gathered to discuss the best use of
diagnostic methods in the region and propose a simplified algorithm.

\section*{Methods}

{\label{methods}}

A modified Delphi method was used to prepare an algorithm using the
iADVISE platform (Within3, OH, USA). Nine experts from Latin American
countries iteratively answered 24 online questions about diagnostic
methods and their application in specific cases for two weeks. The
questions were written by an external microbiologist and infectious
diseases specialist with high expertise in the area and reviewed by a
multidisciplinary panel. The experts also met to review the proposed
algorithm in two online meetings during this period.

The consensus level was determined for each of the 24 initial questions
using a simple yes/no count. For questions with a low level of agreement
(less than 7/9 matched responses), further discussion was necessary to
reach a consensus. Recommendations were only made if the consensus level
was above this threshold.

\section*{Consensus results}

{\label{consensus-results}}

The proposed algorithm is divided into three parts according to time
after first contact or time after symptom onset (Fig. 1).

The rRT-PCR is recommended as the primary test in the initial 14 days
after symptom onset or close contact. Early sample collection from the
upper respiratory tract minimizes the probability of negative rRT-PCR
test results (Mallett et al., 2020). If negative, rRT-PCR may be
repeated in a different sample, at the discretion of the physician.
Antigen detection tests are most likely to perform well in patients with
high viral loads in the pre-symptomatic (1--3 days before symptom onset)
and early symptomatic phases (within the first 5--7 days of
illness)(World Health Organization, 2020). These tests may be used as an
alternative in high-prevalence settings or special cases when rRT-PCR
tests are unavailable.

The rRT-PCR is the diagnostic test of choice between 8--13 days after
initiation of symptoms. If results are negative, rRT-PCR may be
repeated. In some cases, antibody assays may be used during this period,
but considerations should be taken when the results are negative (false
negative tests are still common in this period), or when IgM is positive
and IgG is negative, raising the possibility of a false positive test
(Deeks et al., 2020).

Fourteen days after symptom onset or close contact, antibody detection
assays are recommended as the initial test for the detection of
SARS-CoV-2 infection in immunocompetent hosts. In most cases, antibody
assays are used to trace contacts or for other epidemiological
reasons(Jayamohan et al., 2020), but may be used for individual
diagnosis in specific circumstances.

\par\null\par\null

\textbf{Figure 1}. \textbf{A simplified alternative diagnostic algorithm
for SARS-CoV-2 suspected symptomatic patients and confirmed close
contacts (asymptomatic)}

\par\null\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=1.00\columnwidth]{figures/Fig-1/Fig-1}

\end{center}
\end{figure}

\textsuperscript{a}Ideal use only in high-prevalence
(\textgreater{}5--10\%) scenarios with symptomatic patients or selected
settings (e.g. emergency rooms, elderly residences, healthcare
personnel, and surgical urgencies). The best timeframe for collection in
asymptomatic individuals is 5--7 days after the close contact. Providers
conducting testing on asymptomatic populations must be aware of the
potential for a presumed false-positive result with an antigen test that
will necessitate confirmation with a subsequent RT-PCR test (Virginia
Department of Health, 2020).

\textsuperscript{b}Consider the interpretation of the result as
''Confirmed exposure to SARS-CoV-2''. In the case of IgM positivity
only, consider as a probable false positive (Kubina and Dziedzic, 2020)
and repeat determination with other methods, such as high-affinity
antibody assays (total immunoglobulins or IgG).

\textsuperscript{c}Consider PCR pooling for population screening with
low pre-test probability (\textless{}10\%) to ensure assay
cost-effectiveness or in negative antigen patients. If the pooling
result is positive, individual RT-PCR must be performed for each pooled
sample, so the maximum recommended pool size is 10 (CDC, 2020a).

\textsuperscript{d}Consider multiplex RT-PCR, including influenza A/B or
respiratory panel with influenza, RSV, and other viral/bacterial/fungal
pathogens (Kim et al., 2020) (Zhu et al., 2020). The presence of other
respiratory viruses does not rule out co-infection by SARS-CoV-2,
therefore this possibility should not be neglected (and should be
thoroughly investigated if the clinical-epidemiological context is
suggestive of such).

\textsuperscript{e}Consider antibody tests if other results are
negative.

\textsuperscript{f}Consider Day 14 of symptoms or Day 21 of close
contact.

Ig, immunoglobulin; PCR, polymerase chain reaction; rRT-PCR, real-time
reverse transcription PCR; SARS-CoV-2, severe acute respiratory syndrome
coronavirus 2; RSV, Respiratory Syncytial Virus



\section*{Discussion}

{\label{478114}}\par\null

\subsection*{Available diagnostic
methods}

{\label{available-diagnostic-methods}}\par\null

\subsection*{\texorpdfstring{\emph{Criteria for choosing tests in
resource-constrained
settings}}{Criteria for choosing tests in resource-constrained settings}}

{\label{618170}}

The World Health Organization (WHO) has published the ASSURED
(Affordable, Sensitive, Specific, User-friendly, Rapid and robust,
Equipment-free, and Deliverable to end-users) criteria (Kosack et al.,
2017) that may be used as a benchmark for identifying the most
appropriate diagnostic tests for resource-constrained settings. However,
these criteria are non-specific and need to be adapted to each
diagnostic need, and not all test methods can be simplified to match the
ASSURED criteria.

Kosack et al. also identified six steps that must be additionally
addressed when selecting an \emph{in vitro} diagnostic test: (a)~define
the test's purpose; (b)~review the market and check each product's
specification; (c)~review the test's regulatory approval; (d)~obtain
data on the diagnostic accuracy of the test under ideal conditions (i.e.
in laboratory-based evaluations); (e)~obtain data on the diagnostic
accuracy of the test in clinical practice; and (f)~monitor the test's
performance in routine use.

These six steps should all be considered when selecting an \emph{in
vitro} diagnostic test for routine use.

\par\null

\emph{}

\subsection*{\texorpdfstring{\emph{Viral detection according to the
clinical
course}}{Viral detection according to the clinical course}}

{\label{680915}}

The detection of viral particles (Mallett et al., 2020) (Siam et al.,
2020) or the corresponding immunological response (Deeks et al., 2020)
varies with post-infection time (Fig. 2). A systematic review concluded
that collecting samples early in the course of disease minimizes the
risk of false-negative results (Mallett et al., 2020).

Another systematic review of immunological response studies summarized
assay results for IgG, IgM, IgA, total antibodies, and IgG/IgM since the
onset of symptoms (Sethuraman et al., 2020). All showed low sensitivity
during the first week (30.1\%, 95\% CI 21.4--40.7), which increased in
the second week (72.2\%, 95\% CI 63.5--79.5), and peaked in the third
(91.4\%, 95\% CI 87.0--94.4) and fourth weeks (96.0\%, 95\% CI
90.6--98.3). Specificity was not evaluated according to time but was
generally high for IgM (99.1\%, 95\% CI 97.5--99.8) and IgG (98.6\%,
95\% CI 96.7--99.5).

\par\null

\textbf{Fig. 2. Estimated variation over time in diagnostic tests for
detection of SARS-CoV-2 infection relative to symptom onset} (modified
from Sethuraman \emph{et al} . 2020)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.84\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textsuperscript{a}Detection only occurs if patients are followed up
proactively from the time of exposure.

Ig, immunoglobulin; PCR, polymerase chain reaction; RT-PCR; real-time
reverse transcription PCR; SARS-CoV-2, severe acute respiratory syndrome
coronavirus 2

\par\null\emph{}

\subsection*{\texorpdfstring{\emph{Real-time reverse transcriptase
polymerase chain reaction
(rRT-PCR)}}{Real-time reverse transcriptase polymerase chain reaction (rRT-PCR)}}

{\label{184590}}

Real-time polymerase chain reaction (rRT-PCR) is the gold-standard
molecular technique for the detection of SARS-CoV-2 viral RNA in all
recommended samples. It targets the following sequences that code for
structural viral proteins: spike (S), membrane (M), envelope (E),
nucleocapsid (N), and RNA-dependent RNA polymerase (RdRP). Both S and N
proteins are highly immunogenic (Ravi et al., 2020). The S proteins
seems to be the major target of neutralizing antibodies for correlated
coronaviruses (Berry et al., 2010). High infectivity of SARS-CoV-2 has
compelled the CDC to publish rRT-PCR primers and probes together with
all relevant literature for public access (Khalaf et al., 2020). The
positive rate of rRT-PCR detection is dependent on the sample type, with
differences between bronchoalveolar lavage fluid (93\%),
fibrobronchoscopy brush biopsy (46\%), sputum (72\%), nasal swabs
(63\%), pharyngeal swabs (32\%), feces (29\%), and blood (1\%) (Wang et
al., 2020). Combining nasopharyngeal and oropharyngeal swabs is now one
of the most commonly used specimen types for diagnosing COVID-19 active
infection (Lai and Lam, 2020). In September 2020, the WHO published a
guideline not recommending saliva as the only specimen type for routine
clinical diagnostics, because of the wide variation in collection
methods (World Health Organization, 2020a).

The virus can be detected at least 48 hours before the onset of symptoms
(pre-symptomatic cases), up to 12--14 days (at least 6--7 days) after
the onset of symptoms in samples from the upper respiratory tract (NP/OP
swabs), and for a median of 20 days in samples from the lower
respiratory tract, including sputum, tracheal aspirate, and
bronchoalveolar lavage (Mallett et al., 2020) (World Health
Organization, 2020a) (Lippi et al., 2020).

Pooling rRT-PCR samples~increases testing efficiency, which may be
particularly helpful in areas with low prevalence and few health
resources, given that only a limited number of tests are available (He
et al., 2020). The idea is to pool samples from several individuals and
test the combined sample with a single test. If the test is negative,
all subjects are negative. If the test is positive, all individuals must
be tested again to find the infected patient(s) (Food and Drug
Administration USA, 2020). The US Food and Drug Administration initially
proposed that five was the maximum number of samples to be pooled for
rRT-PCR, but other studies found that the ideal number of pooled samples
depends on the disease prevalence in the tested population (Hanel and
Thurner, 2020) (Deckert et al., 2020) (Cherif et al.,
2020)\textsuperscript{.} One potential constraint of pooled testing is
that the false-negative rate may increase owing to dilution of positive
samples, therefore high-sensitivity rRT-PCR tests are adequate to
minimize this limitation (Lorentzen et al., 2020). In general, the
larger the pool of specimens, the higher the likelihood of generating
false-negative results (CDC, 2020a).

As with all diagnostic tests, the predictive value of rRT-PCR depends
highly on its specificity, sensitivity, and prevalence of the disease in
the target population (CDC, 2020a) (Table 1). False-negative results may
also result from technical issues, from sampling to amplification,
including thermal inactivation~(Siam et al., 2020). A confirmatory test
(e.g. repeated rRT-PCR) may be warranted if the initial results are
negative, and the clinical characteristics are suggestive of infection
(Lai and Lam, 2020) (Lorentzen et al., 2020) .



\textbf{TABLE 1.}~ \textbf{Correlation between pre-test probability and
test results}\textsuperscript{\textbf{a}}

\par\null\selectlanguage{english}
\begin{table*}[H]
\centering
\large\begin{tabulary}{1.0\textwidth}{CCCCCCCCCC}
 &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  & Pre-test probability\textsuperscript{\textbf{b}}
 & Negative predictive value (NPV)\textsuperscript{\textbf{c}}
 & Positive predictive value (PPV)\textsuperscript{\textbf{d}}
 & Increased likelihood \\
 &  &  &  &  &  & Low & High & Low & False positives \\
 &  &  &  &  &  &  &  &  & True negatives \\
 &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  & High & Low & High & True positives \\
 &  &  &  &  &  &  &  &  & False negatives \\
\end{tabulary}
\end{table*}\textsuperscript{a}Modified from Siam \emph{et al. 2020}

\textsuperscript{b}Hellou \emph{et al}. 2020

LAMP, loop-mediated isothermal~amplification; NAAT, nucleic acid
amplification test; PCR, polymerase chain reaction; rRT-PCR, real-time
reverse transcription PCR

\par\null

\subsection*{\texorpdfstring{\emph{Antigen detection
assay}}{Antigen detection assay}}

{\label{101990}}

Another COVID-19 detection method involves the direct detection of
SARS-CoV-2 viral particles using immunoassays (Ji et al., 2020). The
SARS-CoV-2 nucleocapsid protein may be detected in nasopharyngeal swabs
and urine samples of COVID-19 patients within 3 days of onset of fever
(Diao et al., 2020).

A Cochrane systematic review found that sensitivity varied considerably
across studies (from 0--94\%). Based on eight evaluations in five
studies on 943 samples, the average sensitivity was 56.2\% (95\% CI
29.5--79.8) and average specificity was 99.5\% (95\% CI 98.1--99.9)
(Dinnes et al., 2020). Data for individual antigen tests were limited,
with no more than two studies for any test. There were no studies in
asymptomatic individuals.

For asymptomatic individuals, a non-peer-reviewed study showed that for
a pre-test probability of 5\%, the negative predictive value was 99.6\%
(95\% CI 99.5--99.7) and the positive predictive value was 81.5\% (95\%
CI 65.0--93.2) (Alemany et al., 2020). At this pre-test probability, the
estimated number of false-negative and false-positive values per
thousand tests were 4 (95\% CI 3--5) and 12 (95\% CI 4--27),
respectively. The authors stressed the need for confirmatory testing of
positive tests with nucleic acid amplification techniques in these
circumstances (Alemany et al., 2020).

In comparison with rRT-PCR, rapid antigen detection tests tend to have a
lower sensitivity, and owing to the increased risk of false-negative
results, some authors consider such tests only as an adjunct to rRT-PCR
tests (Siam et al., 2020). Alternatively, antigen detection tests have
the advantage of being simple to perform and can play a role in settings
where accessibility to rRT-PCR tests is limited or in symptomatic
patients with a high viral load and within the first 5--7 days after
symptom onset (Lai and Lam, 2020). The viral load is directly related to
the sensitivity of the test (Dinnes et al., 2020).

\par\null

\subsection*{\texorpdfstring{\emph{Antibody
assays}}{Antibody assays}}

{\label{877381}}

Serologic tests are essential because they provide information on
patients who have been infected and already recovered, and asymptomatic
patients who were never diagnosed (Ravi et al., 2020). In a study that
followed the immunological response in COVID-19 patients, three types of
seroconversion were observed: synchronous seroconversion of IgG and IgM
(nine patients), IgM seroconversion earlier than that of IgG (seven
patients), and IgM seroconversion later than that of IgG (ten patients)
(Long et al., 2020). A study profiling the early SARS-CoV-2 humoral
response found that the median time for IgM detection was five days
after symptom onset; IgG was detected at a median of 14 days after
symptom onset (Guo et al., 2020).

For SARS-CoV-2, the IgG and IgM produced specific to the S and N
proteins are of particular diagnostic interest. A study indicates that
the S protein tends to cause a more significant immune response than the
N protein, eliciting neutralizing antibodies (Amanat et al., 2020).
However, other studies argue that the N protein is more immunogenic, as
it is expressed abundantly during active infection (Johns Hopkins Center
for Health Security, 2020).

Some examples of serologic tests to measure patient antibodies include
rapid diagnostic tests (RDTs), enzyme-linked immunoassays (ELISAs),
chemiluminescent immunoassays (CLIAs, not to be confused with the CLIA
acronym: Clinical Laboratory Improvement Amendments), and neutralization
assays (Ravi et al., 2020), performed only at specialized laboratories.
Another review (Deeks et al., 2020) found that some differences were
noted by test technology, with CLIA methods appearing more sensitive
(97.5\%, 95\% CI 94.0--99.0) than ELISA (90.7\%, 95\% CI 83.3--95.0) or
colloidal gold immunoassay (CGIA)-based lateral flow assays (90.7\%,
95\% CI 82.7--95.2) for IgG/IgM (there were also differences in
sensitivity for IgG but no differences for IgM). There was little clear
evidence of differences in specificity between technology types.

Essential considerations for antibody testing include timing of the
test, previous infection, immune status of the individual, and
cross-reaction, which can alter the test results (Siam et al., 2020).

\emph{}

\subsection*{\texorpdfstring{\emph{CRISPR
technology}}{CRISPR technology}}

{\label{591198}}

The CRISPR gene-editing tool has been utilized to construct an accurate,
faster, and simple-to-use SARS-CoV-2 detection test. The DNA
Endonuclease-Targeted CRISPR Trans Reporter (DETECTR) assay is based on
CRISPR--Cas12 and can distinguish SARS-CoV-2 with no cross-reactivity
for related coronavirus strains, using N gene genomic RNA, within 40
minutes (Broughton et al., 2020).

\par\null

\subsection*{\texorpdfstring{\emph{Loop-mediated isothermal~amplification
(LAMP)}}{Loop-mediated isothermal~amplification (LAMP)}}

{\label{910003}}

Loop-mediated isothermal~amplification (LAMP) is a method of isothermal
DNA replication. It utilizes six DNA oligonucleotides that hybridize
with eight different regions of a target molecule in an accelerated
format. Reverse transcriptase can be included to improve sensitivity
within the reaction when detecting an RNA target (RT-LAMP), such as
SARS-CoV-2 RNA (Rabe and Cepko, 2020).

\par\null\par\null

\textbf{Table 2. Comparison of diagnostic options for SARS-CoV-2
detection\textsuperscript{a}}

\par\null\selectlanguage{english}
\begin{table*}[H]
\centering
\normalsize\begin{tabulary}{1.0\textwidth}{CCCCCCCCCCCCC}
 &  &  &  &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  &  &  &  &  &  &  &  \\
 &  &  &  &  &  & Type of test & Specimen sample & Test & Time (min) & Sensitivity (\%) & Specificity (\%) & Cross-reactivity \\
 &  &  &  &  &  & NAAT & Nasopharyngeal swab, sputum, bronchoalveolar lavage fluid & rRT-PCR & 240 & 71--98 & 95 & No \\
 &  &  &  &  &  &  &  & CRISPR & 40 & 97 & 100 & No \\
 &  &  &  &  &  &  &  & LAMP\textsuperscript{b}
 & 30--60 & 75--90 & 93--99 & No \\
 &  &  &  &  &  & Antigen detection & Nasopharyngeal swab & - & 15--30 & 62--92 & 100 & Yes \\
 &  &  &  &  &  & Immune assay & Blood & - & 15--30 & 92--100 & 93--100 & Yes \\
\end{tabulary}
\end{table*}\textsuperscript{a}Modified from Siam \emph{et al. 2020}

\textsuperscript{b}Hellou \emph{et al}. 2020

LAMP, loop-mediated isothermal~amplification; NAAT, nucleic acid
amplification test; PCR, polymerase chain reaction; rRT-PCR, real-time
reverse transcription PCR

\par\null

\textbf{\textsuperscript{}}

\par\null

\subsection*{Special considerations}

{\label{special-considerations}}\par\null

\subsection*{\texorpdfstring{\emph{rRT-PCR vs. antigen
test}}{rRT-PCR vs. antigen test}}

{\label{123067}}

rRT-PCR is the recommended initial test for diagnosing SAR-CoV-2 in
symptomatic patients in international guidelines (Pan American Health
Organization, 2020) (2019-nCoV Working Group. Communicable Diseases
Network Australia., 2020) (CDC, 2020c). However, as the number of
patients presenting with COVID-19 symptoms increases, there has been a
shortage of diagnostic resources, such as swabs, PCR reagents, and RNA
isolation kits, and a growing demand for rapid, onsite diagnostics (Ravi
et al., 2020).

Point-of-care (POC) tests, including rapid antigen detection tests, are
also recommended as an initial test by the CDC (CDC, 2020b),
particularly in the early days of symptoms or in cases of close contacts
in high-risk congregate settings. Infection prevalence at the time of
testing and clinical context both impact pre-test probability (CDC,
2020b) (Table 1) and should be taken into account before and after test
results. Testing of asymptomatic contact cases may be considered after
5--7 days of contact, even if the antigen detection tests are not
explicitly authorized for this use. Asymptomatic cases have been
demonstrated to have viral loads similar to symptomatic cases. A
negative antigen detection test should not remove a close contact
individual from quarantine requirements (World Health Organization,
2020).

Compared with rRT-PCR, antigen detection tests are cheaper, have a
similar specificity, and usually deliver results faster, but have a
lower sensitivity (CDC, 2020b). The choice of test also depends on the
availability of tests and trained personnel, along with the above
factors.

\par\null

\subsection*{\texorpdfstring{\emph{Types and results of immunological
tests}}{Types and results of immunological tests}}

{\label{203959}}

Antibody tests available for laboratory use include ELISA, more advanced
CLIA, and laboratory-independent POC lateral flow assays for rapid
detection of antibodies (such as CGIA), among others (Deeks et al.,
2020).

CLIA methods appear more sensitive (97.5\%, 95\% CI 94.0--99.0) than
ELISA (90.7\%, 95\% CI 83.3--95.0) or CGIA-based lateral flow assays
(90.7\%, 95\% CI 82.7--95.2) for IgG/IgM (Deeks et al., 2020). Tests
that detect antibodies with a high affinity for the SARS-CoV-2 virus are
more likely to indicate neutralizing antibodies (Jayamohan et al.,
2020).

\par\null

\subsection*{\texorpdfstring{\emph{Negative rRT-PCR or antigen detection
tests and the need for
quarantine}}{Negative rRT-PCR or antigen detection tests and the need for quarantine}}

{\label{606137}}

In the case that an individual was only in close contact with an
infected patient and has not developed symptoms, they should complete 14
days of isolation. No tests are necessary, except for particular cases
such as hospitalized patients or for other epidemiological reasons
(World Health Organization, 2020b).

\emph{}

\subsection*{\texorpdfstring{\emph{Image
studies}}{Image studies}}

{\label{893939}}

Chest computed tomography (CT) is considered the primary imaging
diagnostic modality for examining patients with COVID-19 (G\selectlanguage{ngerman}üneyli et
al., 2020). A Cochrane review of radiologic tests (Salameh et al., 2020)
showed that the pooled sensitivity of CT was 86.2\% (95\% CI 71.9--93.8
{[}13 studies, 2,346 participants{]}) and specificity was 18.1\% (95\%
CI 3.71--55.8). In patients with negative RT-PCR tests, Ai \emph{et al.}
(Ai et al., 2020) suggested that a combination of exposure history,
clinical symptoms, typical CT imaging features, and chest CT dynamic
changes should be used to identify COVID-19 cases.

\par\null\par\null

\subsection*{Conclusions}

{\label{conclusions}}

COVID-19 diagnosis is always a cause for uncertainty among physicians,
health professionals, and public health authorities. Our methodology,
involving 24 questions answered by Latin American experts, resulted in a
simplified algorithm involving symptomatic people or close contacts in 3
windows of time (\selectlanguage{english}[?]7 days, 8--13 days, and \selectlanguage{english}[?]14 days).

Even considering the high disparities in healthcare access within the
region, we regard rRT-PCR tests as the standard diagnostic tests for
SARS-CoV-2 infection, from the onset of symptoms until 13 days
afterward. This recommendation is consistent with all main published
guidelines (Pan American Health Organization, 2020) (World Health
Organization, 2020a). Sample pooling should be used in low-resource and
low-prevalence (\textless{}30\%) settings (CDC, 2020a).

We also recommend tests for antigen detection from upper respiratory
tract samples as a simple POC diagnostic test in high-prevalence
settings up to 5--7 days after onset of symptoms (World Health
Organization, 2020). We consider antigen testing a good alternative to
rRT-PCR in this setting, particularly where the molecular tests are not
readily available. Antigen detection tests also appear as a reasonable
option in the CDC guidelines for SARS-CoV-2 detection (CDC, 2020c).

Immunologic assays are not ideal for diagnosis in the early days of
SARS-CoV-2 infection according to WHO and PAHO guidelines (World Health
Organization, 2020a) (Pan American Health Organization, 2020). However,
we suggest that they can be used from 14 days after symptom onset or 21
days after close contact, if asymptomatic, for epidemiological and
contact tracing purposes. Or in some exceptional situations when the
other direct diagnostic tests are repeatedly negative in a patient with
high clinical suspicion and the individual diagnosis is necessary before
that period above mentioned, we recommend the use of antibody assay from
Day 8 onward as an aid to the diagnosis.

Depending on local epidemiology and clinical symptoms, for all suspected
COVID-19 patients, diagnostic testing for other conditions such as
malaria, dengue, typhoid, influenza, and other respiratory diseases
should also be considered (Chi et al., 2020) (United Nations. Department
of Healthcare Management and Occupational Safety and Health, 2020).

In summary, the proposed simplified algorithm aims to support medical
decision-making in Latin America, taking into account published
international guidelines and the region's health access inequalities.

\par\null

\subsection*{Limitations}

{\label{limitations}}

Although based on well-established consensus formation techniques and
drawing on panelists' expertise, these recommendations do not constitute
a statement from the institutions or associations to which these
professionals are affiliated. The main limitations of this expert panel
consensus are selection bias, observer bias, confirmation bias,
publication bias, and cohort effects (different features and pace of the
COVID-19 pandemic in each country of Latin America).

\subsection*{}

{\label{implications}}

\subsection*{Implications}

{\label{implications}}

The proposed algorithm may support COVID-19 diagnosis decision-making in
Latin America, taking into account published international guidelines
and the region's health access inequalities.

\par\null

\subsection*{Acknowledgments}

{\label{acknowledgments}}

Roche Diagnostics LATAM supported the elaboration of this article. Data
was collected by the sponsor and third-party consultants (Within3, OH,
USA, and Conscient Scientific Consultants, SP, Brazil). All authors
contributed to the writing, revision, and approval of the article.
Mariangela Correa from Conscient Scientific Consultants provided medical
writing support.

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