To the Editor:
As of December 10th, 2022, 1.08 million deaths due to COVID-19 were documented in
the United States (US).
1
Although solid organ transplant recipients (SOTRs) are highly susceptible to COVID-19
mortality due to immunosuppression and medical comorbidities,
2
the number of COVID-19 deaths occurring among SOTRs in the US is not well quantified.
Studies reporting on COVID-19 mortality among SOTRs in the US have relied on data
from the Organ Procurement and Transplantation Network (OPTN).
3
,
4
While the OPTN covers all US organ transplants, causes of death (CODs) are unadjudicated
and missing for a substantial proportion of reported deaths.
5
To assess how well OPTN data capture the COVID-19 mortality burden among SOTRs, we
linked a sample of deaths reported by the OPTN in the Scientific Registry of Transplant
Recipients (SRTR) to the National Death Index (NDI). We included deaths occurring
from June 1, 2020 (two months after an OPTN COD code for COVID-19 was introduced)
through December 31, 2020 (last date NDI data were available).
Because SRTR COD data are organized by transplant, there were 14,237 death records
for 12,608 deceased people during this period (11,183 single-organ and 1425 multiple-organ
recipients). Half (n=7151) of these death records were missing an SRTR COD (Table
1
). We submitted 2375 records randomly selected within six COD categories for NDI linkage,
where the sampling fraction varied by SRTR COD category, from 7.9–100.0% (Table 1).
The NDI returned valid matches for 2303 death records (97.0%). Among death records
with an SRTR code or free text indicating a COVID-19 death as the primary COD, NDI
linkage confirmed COVID-19 as the COD in 97.9% and 93.3%, respectively. In addition,
77.8% of death records with COVID-19 listed as a secondary/contributing COD in the
SRTR had an NDI COD of COVID-19. Importantly, 7.9–15.4% of deaths in other sampled
categories were identified by the NDI as due to COVID-19 (Table 1).
Table 1
Comparison of SRTR and NDI causes of death (COD) during June–December 2020, N = 14,237
death records among 12,608 people
Table 1
SRTR COD category
Analyses based on one death record per transplant
Analyses based on one death record per person
c
Total death records
Records sampled for NDI linkage (% sampled)a
NDI records returned
NDI COD indicated on death record as COVID-19,b n (%)
Total deathsc
Estimated COVID-19 deathsc
,
d
Primary COD
COVID-19
1267
100 (7.9)
94
92 (97.9)f
1226
1200
“Other, specify”, with free text specifying COVID-19
120
64 (53.3)
60
56 (93.3)f
115
108
Respiratory or multiorgan failure, or other/unspecified infection
895
470 (52.5)
458
60 (13.1)
740
97
Any other cause
4804
740 (15.4)
723
57 (7.9)
4137
326
Unknown cause or death from non-OPTN source
7151
1001 (14.0)
968
149 (15.4)
6310
971
Secondary/contributing COD
COVID-19
85e
85e (100.0)
81e
63 (77.8)e
,
f
80
62
Total
14,237
2375 (16.7)
2303
414 (18.0)
12,608
2764
COD cause of death, NDI National Death Index, OPTN Organ Procurement and Transplant
Network, SRTR Scientific Registry of Transplant Recipients
a
We sampled fewer records (n = 100, 64, 85) in the SRTR COD categories where we believed
almost all records would be identified as COVID-19 by the NDI, and we sampled more
death records (n = 470, 740, 1001) in all other SRTR COD categories.
b
COVID-19 deaths were identified based on International Classification of Diseases,
Tenth Revision (ICD-10) code U07.1.
c
For the 95 multiple-organ recipients who had SRTR CODs that different across their
death records, we assigned a single COD by preferentially selecting the SRTR COD that
had the highest proportion confirmed to be COVID-19 by the NDI. The order of preference
was as follows (all CODs are primary CODs unless otherwise noted): COVID-19; “Other,
specify”, with free text specifying COVID-19; COVID-19 as a secondary/contributing
COD; unknown cause or death from non-OPTN source; respiratory or multiorgan failure,
or other/unspecified infection; and, finally, any other cause.
d
For each COD category, the estimated number of COVID-19 deaths was obtained by multiplying
the percentages that appear in the column labelled “NDI COD indicated on death record
as COVID-19” by the figures that appear under “Total deaths” (e.g., 0.979 * 1226).
e
The death records in this category overlap with those in the primary COD categories
and are then excluded from the total counts.
f
Considering NDI as the gold standard, these percentages are the positive predictive
values for the SRTR primary or secondary/contributing COD for identifying COVID-19
deaths.
SRTR CODs were consistent across all death records for 1330 (93.3%) of the 1425 multiple-organ
recipients. To estimate the total number of COVID-19 deaths, the proportions of CODs
confirmed to be COVID-19 by the NDI were applied to the number of deceased SOTRs in
each SRTR COD category and summed across categories (Table 1). We thereby estimated
that COVID-19 was the COD in 2764 (21.9%) of the 12,608 SOTRs who died during June-December
2020. Our estimate of 2764 is comparable to Massie et al.’s calculated number of excess
deaths over the same period (2550).
5
In contrast, only 1421 COVID-19 deaths were captured by primary or secondary/contributing
SRTR CODs.
In conclusion, COVID-19 was estimated to be the COD for more than one in five deaths
among SOTRs during the period investigated. Our analysis demonstrates that OPTN/SRTR
data did not capture approximately half of COVID-19 deaths due to missing and incorrectly
assigned CODs. Our findings indicate that 1) future analyses of COVID-19 mortality
among SOTRs should not be solely based on OPTN/SRTR COVID-19 codes and 2) there is
an opportunity for the OPTN/SRTR to improve COD ascertainment.
Funding information
Intramural Research Program of the National Cancer Institute.
This work was conducted under the auspices of the Hennepin Healthcare Research Institute
(HHRI), contractor for the Scientific Registry of Transplant Recipients (SRTR), as
a deliverable under contract no. 75R60220C00011 (US Department of Health and Human
Services, Health Resources and Services Administration, Healthcare Systems Bureau,
Division of Transplantation). The US Government (and others acting on its behalf)
retains a paid-up, nonexclusive, irrevocable, worldwide license for all works produced
under the SRTR contract, and to reproduce them, prepare derivative works, distribute
copies to the public, and perform publicly and display publicly, by or on behalf of
the Government. The data reported here have been supplied by HHRI as the contractor
for SRTR. The interpretation and reporting of these data are the responsibility of
the author(s) and in no way should be seen as an official policy of or interpretation
by SRTR or the US Government.
Disclosures
The authors of this manuscript have no conflicts of interest to disclose as described
by the American Journal of Transplantation.
Declaration of interests
☒ The authors declare the following financial interests/personal relationships which
may be considered as potential competing interests:
Eric A Engels serves as an Associate Editor at the American Journal of Transplantation.