Patrick McColloster, MD, and
Carlos Vallbona, MD
We conducted the first US study
using graphic-output temperature
data loggers in quantifying cold
chain failure. Fifty-four vaccine re-
frigerators of a county outpatient
health system were studied. Forty-
peratures of 2°C to 8°C and 24%
had protracted periods of tempera-
tures less than 0°C. The correlation
between the percentage of refriger-
ators with freezing temperatures
and the pertussis rate for each
health region was r=0.76. The find-
ings suggest that improper vaccine
storage may have contributed to
recent increases in pertussis rates.
(Am J Public Health. 2011;101:46–47.
From 2001 to 2005, the incidence of per-
tussis in Harris County, Texas, increased196%
to a rate of 5.6 cases per 100000.1–3This
elevated rate paralleled a peak in the overall US
incidence.2Domestic studies attempted to ex-
plain the higher incidence by implicating a fall in
immunity among vaccinated adults, unvacci-
nated children causing disease clusters, and
seasonal variation.1However, a Canadian out-
break during the1990s was attributed to exces-
sively cooledpertussis vaccine.4Vaccine spoilage
as a result of cooling has been studied outside
of the United States,5–13although there have
been few domestic studies.7
The purpose of our study was to evaluate the
use of data loggers in quantifying the cold cain
failure rate within the Harris County Hospital
District community health center network.14,15
The health centers are the primary provider of
indigent care services in Harris County; they
support approximately 580000 outpatient visits
We used Extech TH10 digital data loggers
(Extech/Instrusmart, Burlington, VT), which
sample the temperature inside refrigerators
every minute and can store up to 32000 data
points. A built-in Universal Serial Bus port
enabled periodic data downloads to a spread-
sheet and printing a temperature–time graph.
Users can set the data collection frequency and
alarm values. The devices have a 0.1°C reso-
lution with an accuracy of 60.5°C.
We studied 54 refrigerators at 13 commu-
nity health centers (an average of 4 refrigera-
tors per center). Temperature data loggers
were placed in each refrigerator compartment
for a minimum of 6 days and the temperature
was automatically recorded every minute.
The data were then transferred to individual
Excel spreadsheets (Excel 2000).
The percentage of vaccine refrigerator
compartments with freezing temperatures was
calculated for each health region within the
City of Houston, a subset of Harris County.
The results were correlated with the 2005 to
2009 annual average rate of pertussis per
100000 persons in each area.
Twenty-six refrigerator compartments
(48%) maintained a stable temperature within
the 2°C to 8°C range recommended by the
World Health Organization. Thirteen refriger-
ator compartments (24%) had freezing tem-
peratures at some point during the data col-
lection. Ten refrigerators (19%) registered
temperatures from 0.1°C to1.9°C with no
freezing. Five refrigerators had temperatures
greater than 8°C during the data collection.
These data are summarized in Figure1(also see
the table available as a supplement to the online
version of this article at http://www.ajph.org).
Refrigerators that registered freezing levels
had temperatures less than 0°C for an average
of 8.0% of the total time recorded (equivalent
to 2 hours per day). Refrigerators that were
excessively cold but not freezing maintained
temperatures between 0.1°C and 1.9°C for an
average of 25.3% of the total time recorded.
The Pearson correlation between the per-
centages of refrigerator compartments with
freezing temperatures in each health region of
Houston and the 2005 to 2009 annual aver-
age rate of pertussis per 100000 persons in
each area was r=0.76 (P<0.05). These data
are summarized in Table 1.
Six of the 28 refrigerators could not main-
tain a stable temperature regardless of the
thermostat setting and were not suitable
FIGURE 1—Percentage of Refrigerators Within and Outside of Correct Temperature Range
Houston, Texas, 2005–2009
RESEARCH AND PRACTICE
46 | Research and Practice | Peer Reviewed | McColloster and Vallbona
American Journal of Public Health | January 2011, Vol 101, No. 1
for storing vaccines (figure available as a sup- Download full-text
plement to the online version of this article at
http://www.ajph.org). Only1was recognized as
defective using the Vaccines for Children rec-
ommended standard of recording tempera-
tures from digital thermometers twice every
Manufacturer recommendations for the
storage of acellular pertussis vaccine advise
discarding any vaccine exposed to tempera-
tures less than 0°C since the vaccine is inacti-
vated upon freezing.15,16Approximately 24% of
the refrigerators studied exposed vaccines to
considerable durations of subzero temperatures.
The periods of freezing temperatures typically
occurred on weekends and nights.
The Harris County Hospital District adhered
to the current vaccine storage guidelines rec-
ommended by Vaccines for Children and in-
ternal audits have complied with a Joint Com-
mission survey conducted during the study.
The inadequate storage would not have been
detected or quantified without the use of the
digital temperature data loggers. The graphic
output provided by the loggers has allowed us
to interpret temperature data in a manner not
possible with the traditional twice-daily tem-
Our findings raise the possibility that the
recent increase in cases of pertussis may be
partially the result of improper storage of
acellular pertussisvaccine. The currentstandard
adequate to maintain proper vaccine storage.
Given the low cost of these devices ($35–45),
adoption of digital data loggers for maintaining
the cold chain should be considered. j
About the Authors
Patrick McColloster and Carlos Vallbona are with Baylor
College of Medicine, Houston, TX.
Correspondence should be sent to Patrick McColloster,
1615 N. Main Street, Houston, TX 77009 (e-mail:
email@example.com). Reprints can be ordered at
http://www.ajph.org by clicking the ‘‘Reprints/Eprints’’ link.
This article was accepted March 28, 2010.
P. McColloster originated the study, conducted the
research, and wrote the article. C. Vallbona edited the
article and helped secure funding.
We acknowledge the Department of Family and Com-
munity Medicine at Baylor College of Medicine for
providing the funds used to purchase the data loggers.
Note. The authors have no financial interests or
ownership in any companies related to the study.
Human Participant Protection
The institutional review board at Baylor College of
Medicine granted approval for the study.
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TABLE 1—Percentage of Vaccine
Refrigerators with Freezing
Temperatures and the Pertussis Rate:
Houston, Texas, 2005–2009
North East 80 6.3
Central West56 3.5
South West45 3.0
Source. Pertussis data provided by the City of Houston
Public Health Department.
RESEARCH AND PRACTICE
January 2011, Vol 101, No. 1 | American Journal of Public Health
McColloster and Vallbona | Peer Reviewed | Research and Practice | 47