Reply to the enhancing the accuracy of seroprevalence studies: Reassessing pertussis infection rates in Eastern China during the COVID-19 pandemic

KEYWORDS:

• Pertussis
• sero-epidemiology
• vaccine
• factors

Dear Editor, we would like to express our gratitude for raising concerns regarding the accuracy and reliability of the ELISA detection method used in the original study “enhancing the Accuracy of Seroprevalence Studies: Reassessing Pertussis Infection Rates in Eastern China During the COVID-19 Pandemic,”¹ as well as the potential impact of these concerns on the validity of the research findings. In this study of the seroepidemiology of Immunoglobulin G antibodies against pertussis toxin and filamentous hemagglutinin in the east of China during the COVID-19 pandemic,² we utilized the Pertussis Toxin (PT) Antibody Assay Kit produced by Zhengzhou test Biotech Co., Ltd. The kit’s instruction manual indicates that the detection principle involves the microplate coated with PT antigen, forming a solid-phase carrier that reacts with specific antibodies (anti-PT) present in the sample to be tested. This forms an antigen-antibody complex that is adsorbed onto the solid phase. Subsequently, enzyme-labeled anti-human IgG is added, resulting in the formation of an immune complex. After washing, the chromogen is added, and the color develops. The absorbance value is determined using an enzyme-linked immunosorbent assay reader. The intensity of the color is directly proportional to the antibody content. The results are calculated using a four-parameter fitting method (Logistic curve four-parameter fitting). A standard curve is established with the concentration values of the standard samples on the x-axis and the logarithmic values (log) of the standard sample OD values on the y-axis. The absorbance value of the sample to be tested is substituted into the equation to calculate the corresponding concentration value of the serum antibody. The clinical research results of the kit show that out of 1,342 test samples (due to insufficient sample volume, 1,306 samples for PT and 1,307 samples for Filamentous Hemagglutinin (FHA) were included in the clinical trial statistical analysis), there was a significant positive correlation between the results determined by this kit and the standard method (four-parameter logarithmic fitting of dual parallel lines) used by the China Food and Drug Inspection and Research Institute.

However, it is regrettable that the kit does not provide the sensitivity and specificity values. Through subsequent communication with the R&D personnel of the manufacturer, we were informed that both the sensitivity and specificity of the kit are above 98.0%. Here, the estimated rate of pertussis infection is adjusted based on seroprevalence × (99.6%/(99.6% + 0.4%)) = Adjusted estimated rate of pertussis infection. The adjusted estimated rate of pertussis infection = Estimated rate of pertussis infection based on seroprevalence × (99.6%/100%) = Estimated rate of pertussis infection based on seroprevalence.³ Therefore, after adjusting for sensitivity and specificity, the estimated pertussis infection rate based on the seropositive rate remains unchanged, as the provided sensitivity and specificity values are very high and do not significantly affect the calculation results.

Furthermore, we will conduct additional research. We will reevaluate all serum samples using ELISA kits (Institut Virion/Serion GmbH, Germany) (ELISA kit sensitivity: >99%, specificity: 98.6%) to verify and improve the accuracy and reliability of the detection method, ensuring that future serological epidemiological studies can provide more accurate data.

Disclosure statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Additional information

Funding

This manuscript was funded by the Jiangsu Health Development Research Center Open Project [grant number JSHD2022043], the Jiangsu Provincial Geriatric Health Research Project [grant number LKM2023005], Suqian Sci&Tech Program [grant number SY202312] and Jiangsu Provincial Health Commission Preventive Medicine and Hematology Prevention Research Project [grant number Ym2023099].