**1. Introduction**

Common variable immunodeficiency (CVID) is the most prevalent symptomatic primary immunodeficiency (PID) in humans [1] and is included in the antibody predominant immunodeficiency category according to the International Union of Immunological Societies (IUIS) classification [2].

CVID is considered a complex group of PID due to its clinical and immunological heterogeneity, and the underlying genetic cause is mostly unknown. Genetic defects are detected in approximately 25% of the cases, involving defects in humoral and cell-mediated immunity [3,4]. Diagnostic criteria for CVID, according to the European Society for Immunodeficiencies (ESID), include a decrease in IgG (at least two standard deviations below the

**Citation:** Díaz-Alberola, I.; Gutiérrez-Bautista, J.F.; Espuch-Oliver, A.; García-Aznar, J.M.; Anderson, P.; Jiménez, P.; Hidalgo-Tenorio, C.; López-Nevot, M.Á. Incidence, Management Experience and Characteristics of Patients with Giardiasis and Common Variable Immunodeficiency. *J. Clin. Med.* **2022**, *11*, 7007. https://doi.org/10.3390/ jcm11237007

Academic Editor: Ilaria Cavazzana

Received: 24 October 2022 Accepted: 25 November 2022 Published: 27 November 2022

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mean for age) and a marked decrease in at least one of the isotypes IgM or IgA, an impaired antibody production to vaccination or low percentage of switched memory B cells (<70% of age-related normal value), clinical manifestations of recurrent infections, autoimmune diseases or lymphoproliferation, the onset of clinical immunodeficiency at more than two years of age and the exclusion of other causes of hypogammaglobulinemia [5]. The defect in plasma cell differentiation causes hypogammaglobulinemia and abnormalities of circulating B cell subsets, with a normal or low absolute count of B cells [6]. Although profound T cell defects are not detected, alterations in their frequency and function can be found [7].

Severe and recurrent infections are the clinical hallmark in CVID patients. *Giardia lamblia* is the most commonly identified gastrointestinal pathogen in CVID, followed by *Campylobacter jejuni* and *Salmonella species* [8]. *Giardia lamblia* (also termed *G. duodenalis* or *G. intestinalis*) is a flagellated parasitic protozoan with a lifecycle divided into two phases: the dormant infectious cyst and the proliferating trophozoite [9] (Figure 1). Clinical manifestations of *Giardia* infection are diverse, ranging from asymptomatic cases to diarrhea, abdominal pain, nausea, anemia, malabsorption, or weight loss. Classic diagnosis is performed by microscopic detection of trophozoites or cysts in stool samples, but in recent years, rapid immunochromatographic antigen tests and more sensitive real-time polymerase chain reaction (PCR) panels have appeared [10].

**Figure 1.** Lifecycle of *Giardia lamblia*. Infectious cysts are ingested via contaminated food or water, or by direct ingestion. In the human gastrointestinal tract, cysts excyst to release trophozoites, which cause disease, in part, by promoting the disruption of the intestinal epithelial barrier. Both the cysts and trophozoites can be detected in the stool, although the trophozoites released do not survive long.

5-Nitroimidazole compounds, such as tinidazole or metronidazole, are the most common first-line treatment for *Giardia* infection [11]. Nitroimidazoles are usually also effective in CVID patients. However, CVID patients have a higher risk of chronification, reinfection and relapse rate due to their immunodeficiency status or malabsorption syndrome, and often require prolonged treatment [12,13].

Nitroimidazole-refractory giardiasis is increasing in the general population, linked with parasite drug resistance and host factors [14–16]. Nevertheless, few cases of refractory giardiasis in CVID patients have been published to date [17]. Currently, resistance *Giardia* detection is not possible to perform in most laboratories, and there is no standard treatment for refractory giardiasis. Empirical treatments are currently used, highlighting the use of a nitroimidazole other than metronidazole in monotherapy or with another drug, or other agents such as quinacrine or paromomycin [18].

The aim of this study was to determine the incidence of *Giardia* infection in patients diagnosed with CVID at our hospital center, describing our management experience and their demographic, clinical, immunogenetic, and immunological characteristics. In addition, we have performed a literature review of previous reports of *Giardia* infection in CVID patients.

#### **2. Materials and Methods**

#### *2.1. Subjects of Study*

Patients diagnosed with CVID and *Giardia lamblia* infection in the University Hospital Virgen de las Nieves between 2000 and 2021 were recruited for this study. The diagnosis of CVID was established based on the ESID criteria [5], excluding patients with other types of antibody immunodeficiencies, secondary antibody deficiencies, and T-cell deficiency.

*Giardia* infection was determined by stool *Giardia* antigen detection test, microscopy observation, molecular technique, or a combination of these, in patients with suggestive symptoms as described below. Refractory giardiasis was considered when *Giardia* persisted after one or more strategic treatments. We collected demographic and clinical data, family and personal history, and immunoglobulin levels at CVID diagnosis. Furthermore, we performed other immunological and immunogenetics assays during subsequent follow-ups of each patient. This study was reviewed and approved by the regional ethics committee (Portal de Ética de la Investigación Biomédica de Andalucía, PEIBA, code: 1206-N-22). Patients or their legal representatives provided their written informed consent to participate.

#### *2.2. Immunological Evaluation*

Serum immunoglobulins (Ig) levels (IgG, IgA and IgM) were measured by immunoturbidimetry using the automatic analyzer Alinity c system (Abbott Laboratories, Chicago, IL, USA). For cellular evaluation, EDTA whole blood samples were collected. Lymphocyte subpopulations (CD4+ T, CD8+ T, B and NK cells) were performed using BD Trucount tubes and the BD Multitest 6 Color BTNK kit (BD Biosciences, San Diego, CA, USA), which included the following mixtures of fluorophore-conjugated monoclonal antibodies (mAb): anti-CD45-PerCP-Cy5.5, anti-CD3-FITC, anti-CD8-APC-Cy7, anti-CD4-PE-Cy7, anti-CD19-APC, and anti-CD16+CD56-PE. B cell phenotype was performed with an eightcolor panel of the following mAb: anti-CD45-APC-H7, anti-CD19-V500, anti-CD10-V450, anti-CD38-PE-Cy7, anti-CD21-PE, anti-CD27-PerCP-Cy5, anti-IgD-FITC, and anti-IgM-APC (BD Biosciences, San Diego, CA, USA), following EURO-Class classification. Cells were acquired on a BD FACSCanto II Flow Cytometer (BD Biosciences, San Diego, CA, USA), and the InfinicytTM22.0 software was employed for multiparametric analysis (Cytognos SL, Salamanca, Spain).
