Am. J. Trop. Med. Hyg., 85(6), 2011, pp. 1144–1145
Copyright © 2011 by The American Society of Tropical Medicine and Hygiene
Several studies have highlighted the use of rapid influenza
testing to improve early detection of epidemics and conduct
outbreak responses. 1, 2 Rapid influenza testing can be used to
identify patients with influenza in a timely manner and influ-
ence clinical treatment. 3, 4 Although rapid testing for influenza
has been demonstrated to be less sensitive when compared
with the polymerase chain reaction (PCR), 5 it could be an
attractive diagnostic tool in resource-limited settings lack-
ing laboratory capabilities to identify influenza by culture
or molecular techniques. There is limited data on the use of
rapid influenza testing in Southeast Asia and regions where
numerous etiologies of acute febrile illness are endemic
and could require prompt treatment (e.g., malaria, dengue,
Hospital-based and clinic based influenza surveillance was
established to ascertain the etiologies contributing to acute
febrile illness in patients in Cambodia. 6 We report the per-
formance of a rapid influenza test conducted at the sites of
enrollment to identify influenza as an etiology of febrile illness
during December 2006–May 2008 in Cambodia. Outpatients
were initially recruited from two referral hospitals, but dur-
ing the course of the study, seven additional healthcare facili-
ties were added; two in August 2007, one in October 2007, one
in December 2007, one in February 2007, one in March 2008,
and one in April 2008. Study sites were located ≤ 50 km of
Phnom Penh in southcentral Cambodia.
Patients were clinically evaluated by a physician or medi-
cal assistant and recruited for study participation if they met
inclusion criteria: at least 24 hours of fever (a measured tym-
panic membrane temperature > 38.0°C), were ≥ 2 years of age,
and after medical examination, had no obvious source of infec-
tion. Influenza-like illness was defined as fever (> 38.0°C) with
cough and/or sore throat. Eligible subjects voluntarily enrolled
in accordance with an Institutional Review Board protocol
approved by U.S. Naval Medical Research Unit No. 2 in com-
pliance with all applicable Federal regulations governing the
protection of human subjects and the National Ethics Commit-
tee of the Royal Kingdom of Cambodia, Ministry of Health.
For each enrolled patient, one throat and one nasal swab
was collected and placed in a vial containing 2–3 mL of virus
transport medium. All inoculated vials were kept at 4°C
until received by the laboratory 24–72 hours after collection.
Medical personnel were trained by study investigators by
using the manufacturer’s instructions on the proper collection
of a nasopharyngeal swab and interpretation of the QuickVue
Influenza A+B Test (Quidel Inc., San Diego, CA). Color digi-
tal photographs of all rapid test results were taken and for-
warded for laboratory supervisor’s confirmation. RNA was
extracted from nasal and throat swabs by using QIAamp viral
RNA mini kits (QIAGEN, Hilden, Germany) according to
the manufacturer’s instruction and stored at –70°C. Influenza
virus genome was detected by using a reverse real-time PCR
(Centers for Disease Control and Prevention, Atlanta, GA)
developed to detect influenza A and B viruses and influ-
enza A viruses of H1, H3, and H5 subtypes and performed as
A total of 1,327 patients were enrolled during December
2006–May 2008. Among the participants, the median age was
10 years (interquartile range [IQR] = 5–22 years) and 50%
were male. The median time of illness prior to presentation
for healthcare services was 3 days (IQR = 2–3 days). During
this period, 261 (19.7%) enrollees were identified as influenza
positive by RT-PCR, and 147 participants were influenza posi-
tive by rapid test. Among the 147 rapid test–positive results,
136 had concordant results by RT-PCR. Overall, the sensitiv-
ity and specificity of the Quickvue influenza rapid test com-
pared with PCR was 52.1% and 92.5%, respectively. Among
the 136 concordant results, 72 (52.9%) were influenza A and
64 (47.1%) were influenza B. Sensitivity for influenza A and B
was 47% and 57%, respectively. One case identified as rapid
influenza A positive at the field site was later confirmed to be
Among PCR-positive influenza patients, the median age of
rapid test–positive patients was 8 years (IQR = 5–12 years) and
the median age of rapid test–negative patients was 10 years
(IQR = 5–17 years). There was a significant difference between
the sensitivities of the rapid test between age groups, 56.9%
among patients 2–18 years of age and 22.2% among patients
> 18 years of age ( P = 0.0001). The median day of presenta-
tion for health care services was 3 days for rapid test positive-
patients (IQR = 2–3 days) and rapid test–negative patients
Short Report : Rapid-Test Based Identification of Influenza as an Etiology of
Acute Febrile Illness in Cambodia
Matthew R. Kasper ,* Shannon D. Putnam , Ly Sovann , Chadwick Y. Yasuda , Patrick J. Blair , and Thomas F. Wierzba
U.S. Naval Medical Research Unit No. 2, Jakarta, Indonesia; Communicable Disease Control Department, Ministry of Health,
Phnom Penh Cambodia; U.S. Naval Medical Research Unit No. 2, Phnom Penh, Cambodia
Abstract. Influenza can be manifested as an acute febrile illness, with symptoms similar to many pathogens endemic
to Cambodia. The objective of this study was to evaluate the Quickvue influenza A+B rapid test to identify the etiology of
acute febrile illness in Cambodia. During December 2006–May 2008, patients enrolled in a study to identify the etiology of
acute febrile illnesses were tested for influenza by real-time reverse transcriptase PCR (RT-PCR) and Quickvue influenza
A+B rapid test. The prevalence of influenza was 19.7% by RT-PCR. Compared with RT-PCR, the sensitivity and specific-
ity of the rapid test were 52.1% and 92.5%, respectively. The influenza rapid test identified the etiology in 10.2% of enroll-
ees and ≥ 35% during peak times of influenza activity. This study suggests that rapid influenza tests may be useful during
peak times of influenza activity in an area where several different etiologies can present as an acute febrile illness.
* Address correspondence to Matthew R. Kasper, Department of
Bacteriology, U.S. Naval Medical Research Unit 6, Lima, Peru,
Unit 3230, DPO, AA 34031. E-mail: email@example.com
USE OF INFLUENZA RAPID TEST IN CAMBODIA
(IQR = 2.5–4 days). A comparison based on day of fever pre-
sentation identified a significant difference among patients
presenting at days 0–3 (61.1%) and day 4 (22.4%) ( P < 0.0001).
There was no significant difference in rapid test results based
on a clinical presentation with influenza-like illness; 74.8% of
rapid test–positive patients and 79.3% of rapid test–negative
patients had influenza-like illness ( P = 0.39).
Among 1,327 patients enrolled who had an acute febrile
illness, use of an influenza rapid test resulted in 136 (10.2%)
patients who were diagnosed with influenza at the time of
their health care visit. During the peak of influenza activ-
ity (August–December 2007), 6 influenza rapid tests identi-
fied 20–35% of the acute febrile cases as influenza infections.
There was a significant difference in the sensitivity of the rapid
test when used at times of peak influenza activity compared
with when influenza was not circulating (55.6% versus 25.1%,
respectively; P = 0.002).
In this study, the overall sensitivity of the influenza rapid
test was similar to those of published studies. 5, 7– 9 The cost of
influenza PCR testing (US $21–25/test) and infrastructure
requirements prevent its routine clinical use in Cambodia.
A laboratory-based surveillance program that monitors influ-
enza activity in a region could determine times to implement
rapid testing beyond the influenza surveillance sentinel sites
to help manage and diagnose illnesses. Limiting the use of
rapid tests (US $7–12/test) 10 to times determined by a labo-
ratory-based surveillance program would be a more cost-
effective alternative than year-round testing.
This study was conducted in a region endemic to several
causes of acute febrile illness (e.g., dengue, malaria, typhoid)
that can present with similar symptoms and can make a clini-
cal diagnosis of disease difficult. This study suggests that rapid
influenza tests may be useful during peak times of influenza
activity or during outbreaks in an area where several different
etiologies can present as an acute febrile illness.
Received June 20, 2011. Accepted for publication August 30, 2011.
Acknowledgments: We thank the clinicians and medical staff at the
field sites in Cambodia for their assistance in enrolling and sampling
patients and laboratory personnel at the U.S. Naval Medical Research
Unit No. in Phnom Penh and the Centers for Disease Control and
Prevention for participating in the study.
Financial support: This study was supported in part by grants from
the Influenza Division of the U.S. Centers for Disease Control and
Prevention and the U.S. Department of Defenses’ Global Emerging
Infection Systems, a division of the Armed Forces Health Surveillance
Disclaimer: The views expressed in this article are those of the
authors and do not necessarily reflect the official policy or position
of the Department of the Navy, Department of Defense, or the U.S.
Disclosure: Several of the authors are military service members. This
work was prepared as part of our official duties. Title 17 U.S.C. §105
provides that “Copyright protection under this title is not available
for any work of the United States Government.” Title 17 U.S.C. §101
defines a U.S. Government work as a work prepared by a military ser-
vice member or employee of the U.S. Government as part of that per-
son’s official duties.
Authors’ addresses: Matthew R. Kasper, Shannon D. Putnam, and
Patrick J. Blair, Department of Bacteriology, U.S. Naval Medical
Research Unit 6, Lima, Peru, Unit 3230, DPO, AA, E-mails: matthew
.firstname.lastname@example.org , email@example.com , and Patrick.blair@
med.navy.mil . Ly Sovann, Communicable Disease Control Department,
Ministry of Health, Phnom Penh Cambodia, E-mail: sovann_ly@
online.com.kh . Chadwick Y. Yasuda and Thomas F. Wierzba, U.S.
Naval Medical Research Unit No. 2, Phnom Penh, Cambodia, E-mail:
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