This preliminary study was conducted at the adult ADHD outpatient center of the San Luigi Gonzaga University Hospital (Orbassano, Turin, Italy), between July 1, 2019 and September 1, 2019, on a consecutive sample of patients newly diagnosed with adult ADHD according to DSM-IV-TR criteria (age > 18 years). According to the outpatient service routine, all patients had been screened for adult ADHD using the Adult ADHD Self Reporting Scale (ASRS-1.1) screener, and then the DSM-IV ADHD diagnosis was confirmed through the Diagnostic Interview for Adult ADHD (DIVA 2.0). The severity of ADHD symptoms was rated by Adult ADHD Investigation Rating Scale (AISRS).
All patients were asked to participate in the study signing a written informed consent and a unique identification code was assigned to each patient, in order to maintain data anonymity and patient confidentiality. The research protocol of the present observational study was approved by the Research Ethics Committee of the San Luigi Gonzaga University Hospital (Orbassano, Turin, Italy), therefore the study was conducted in accordance with the Helsinki Declaration.
During the assessment process, information about the history of both infections and psychiatric disorders were collected and patients were also assessed for other psychiatric disorders through an in-depth psychiatric interview. Recurrent infections in childhood (i.e., under 12) were defined as at least three symptomatic episodes of infection with fever (e.g., tonsillitis, adenoiditis, glomerulonephritis, or others) per year for at least one year.
Blood samples from patients were collected in potassium ethylenediaminetetraacetic acid (EDTA) - containing tubes (BD Vacutainer® spray-coated K2EDTA, Becton, Dickinson and Company, Franklin Lakes, NJ, USA) at the end of each recruitment. Plasma was separated by centrifugation at 24,104 x g at 4°C for 10 min and immediately stored at -80°C ready for analyses.
Commercial, ready-to-use, microwell ELISA kits were used for the quantitative determination of plasma concentration of ASO (Cat. No MBS038268, MyBioSource Inc., San Diego, USA), anti-DNase B (Cat. No MBS7226468, MyBioSource Inc., San Diego, USA), and ABGA (Cat. No MBS706650, MyBioSource Inc., San Diego, USA). Sample absorbance values were detected in a 96-multiwell plate reader (Model 680 Microplate Reader, Bio-Rad, Milan, Italy) using dual-wavelength recording modes at 450 nm and 655 nm (the latter used as reference). ELISA protocols instructions, and threshold values for adults provided by the manufacturer were adopted. . Thereby, the following values defined patient positivity: ASO > 200 U/ml; anti-DNase B > 86 ng/ml; ABGA > 1.18 (as the ratio referred to the negative control optical density) but absolute titers values were also collected as continuous variables.
Clinical assessment tools
The ASRS 1.1  is a six-item self-report screener for adult ADHD, based on the DSM-IV-TR criteria. It was developed by the World Health Organization (WHO) and then validated internationally . The screening is considered positive when at least four answers are above cut-off value.
The DIVA 2.0  is a validated  semistructured interview to assess the adult patients, according to the DSM-IV criteria. It investigates DSM-IV inattentive and hyperactivity/impulsivity symptoms (criterion A) in both childhood and adulthood, using several real-life examples to support each question inquiring about 18 DSM-IV criteria. It also includes explicit questions for age at onset (i.e., the presence of symptoms before the age of seven years, criterion B) and other primary psychiatric and/or substance use disorders (which could better explain the reported symptoms, criterion E). The last section consists in an in-depth evaluation of the main areas of functioning impacted by ADHD symptoms (criteria C and D). Furthermore, the collateral information should be reported in both content and source (i.e., the presence of parents/third parties; school reports).
The AISRS is a validated  18-item scale matching the DSM-IV criteria. It is divided into two subscales of nine items each, investigating inattentive and hyperactivity/impulsivity, respectively. The items are provided with examples to minimize interrater variability. The scoring system ranges from zero (none) to three (severe). The maximum score for each subscale is 27 points, with a maximum total score of 54.
All analyses and calculations were performed using RStudio for MAC OS (Version 1.1.383, RStudio Inc., Boston, MA).
The positivity rate for every titer was calculated. The distributions of continuous variables were tested by Shapiro-Wilk’s test. A p-value of 0.05 was used to designate statistical significance. Mean and standard deviation (SD) were used to report normally distributed variables, whereas median (Mdn) and interquartile range (IQR) were used for nonnormally distributed ones.