Discussion
We found that kidney transplant recipients developed an antibody
response following COVID-19; the mean antibody level and the
seropositivity rate were similar to that of the control group. To the
best of our knowledge, the largest report about antibody response in
kidney transplant recipients was from Azzi et al. [9]. They examined
69 kidney transplant recipients who had an RT-PCR confirmed COVID-19
diagnosis, and 55 (80.0%) of them have positive antibody response. They
used the same test as our study to measure antibody levels. They
measured the antibody response following a median of 44 days following
RT-PCR positivity. Hartzell et al. examined anti-SARS-Cov2 IgG
antibodies in 16 kidney transplant recipients following a mean of 16.1
days of RT-PCR testing; antibody positivity rate was reported as 60.0%
and 63.6% depending on immunosuppressive drug use [17]. Burack et
al. examined 39 kidney transplant recipients and found an antibody
positivity of 41.0% [7].
According to our data infection in a household member and high BMI was
associated with COVID-19 infection in kidney transplant recipients.
Previous studies showed an association between high BMI and severe
COVID-19 [18]. However, it is not clear whether the risk of COVID-19
increases with high BMI [19-22]. A recent study showed that the
prevalence of obesity in patients hospitalized with COVID-19 is higher
than the worldwide prevalence of obesity [23].
In kidney transplant recipients who did not have positive RT-PCR
testing, we found a similar SARS-CoV-2 IgG antibody positivity rate to
our controls. In line with our results, a recent study reported that the
seroprevalence rate was 6.6% in asymptomatic people [24]. In
another study SARS-CoV-2 seroprevalence in healthy blood donors was
reported as 3% [25].
We did not identify any specific risk factor for lack of seroconversion
following COVID-19. However, we noted a trend toward lower antibody
levels in patients who had a longer post-infection duration. A similar
observation was reported by Benotmane et al. [26]. They examined 29
kidney transplant recipients hospitalized for COVID-19 and measured
antibody levels up to 6 months after COVID-19. During the follow-up,
20.7% of the patients become seronegative. A considerable IgG reduction
was observed in patients treated with calcineurin inhibitors and
steroids. No statistically significant difference was found regarding
disease severity.
Our study has some limitations; we did not formally screen all patients;
we might have overlooked some patients who had severe COVID-19 and died.
However, it is unlikely that we missed mild cases because most of the
patients were in close telephone contact with transplant coordinators
during this period. Another limitation of this study is that the date of
infection was defined as the date of PCR positivity, as opposed to the
date of symptom onset. Since transplant recipients may exhibit prolonged
shedding of the virus, the date of PCR positivity may not always be an
accurate estimate of infection onset. Kidney transplant recipients and
controls had different distribution characteristics regarding duration
between COVID-19 and antibody testing, all the controls were tested for
antibodies following at least four weeks, and no control was tested
following more than 12 weeks. However, the distribution of transplant
recipients between different IgG testing duration categories was
homogenous. Finally, we did not examine parameters related to cellular
immunity.