Co-detection of respiratory pathogens among ILI patients: characterization of samples collected during the 2018/19 and 2019/20 pre-pandemic seasons.

Influenza-like illness (ILI) patients co-detected with respiratory pathogens exhibit poorer health outcomes than those with single infections. To address the paucity of knowledge concerning the incidence of concurrent respiratory pathogens, their relationships, and the clinical differences between patients detected with single and multiple pathogens, we performed an in-depth characterization of the oropharyngeal samples of primary care patients collected in Genoa (Northwest Italy), during winter seasons 2018/19-2019/20.The apriori algorithm was employed to evaluate the incidence of viral, bacterial, and viral-bacterial pairs during the study period. The grade of correlation between pathogens was investigated using the Phi coefficient. Factors associated with viral, bacterial or viral-bacterial co-detection were assessed using logistic regression.The most frequently identified pathogens included influenza A, rhinovirus, Haemophilus influenzae and Streptococcus pneumoniae. The highest correlations were found between bacterial-bacterial and viral-bacterial pairs, such as Haemophilus influenzae-Streptococcus pneumoniae, adenovirus-Haemophilus influenzae, adenovirus-Streptococcus pneumoniae, RSV-A-Bordetella pertussis, and influenza B Victoria-Bordetella parapertussis. Viruses were detected together at significantly lower rates. Notably, rhinovirus, influenza, and RSV exhibited significant negative correlations with each other. Co-detection was more prevalent in children aged < 4, and cough was shown to be a reliable indicator of viral co-detection.Given the evolving epidemiological landscape following the COVID-19 pandemic, future research utilizing the methodology described here, while considering the circulation of SARS-CoV-2, could further enrich the understanding of concurrent respiratory pathogens.

Improving Influenza Vaccination Coverage in Patients with Cancer: A Position Paper from a Multidisciplinary Expert Group.

Patients with cancer can be immunocompromised because of their disease and/or due to anticancer therapy. In this population, severe influenza virus infections are associated with an elevated risk of morbidity and mortality. Influenza vaccination is therefore highly recommended in cancer patients, including those receiving anticancer therapy. However, vaccination coverage remains far below the recommended target for vulnerable subjects. Six specialists in oncology, hematology, immunology, and public health/vaccinology convened with the objective of developing strategies, based on evidence and clinical experience, for improving influenza vaccination coverage in cancer patients. This viewpoint provides an overview of current influenza vaccination recommendations in cancer patients, discusses barriers to vaccination coverage, and presents strategies for overcoming said barriers. New immunization issues raised by the COVID-19 pandemic are also addressed. Future directions include improving public education on influenza vaccination, providing the media with accurate information, improving knowledge among healthcare professionals, improving access to vaccines for cancer patients, co-administration of the influenza and COVID-19 vaccines, increased collaboration between oncologists and other health professionals, increased accessibility of digital vaccination registries to specialists, shared information platforms, and promoting immunization campaigns by healthcare systems with the support of scientific societies.

Pneumocystis jirovecii pneumonia in intensive care units: a multicenter study by ESGCIP and EFISG.

BACKGROUND: Pneumocystis jirovecii pneumonia (PJP) is an opportunistic, life-threatening disease commonly affecting immunocompromised patients. The distribution of predisposing diseases or conditions in critically ill patients admitted to intensive care unit (ICU) and subjected to diagnostic work-up for PJP has seldom been explored. MATERIALS AND METHODS: The primary objective of the study was to describe the characteristics of ICU patients subjected to diagnostic workup for PJP. The secondary objectives were: (i) to assess demographic and clinical variables associated with PJP; (ii) to assess the performance of Pneumocystis PCR on respiratory specimens and serum BDG for the diagnosis of PJP; (iii) to describe 30-day and 90-day mortality in the study population. RESULTS: Overall, 600 patients were included in the study, of whom 115 had presumptive/proven PJP (19.2%). Only 8.8% of ICU patients subjected to diagnostic workup for PJP had HIV infection, whereas hematological malignancy, solid tumor, inflammatory diseases, and solid organ transplants were present in 23.2%, 16.2%, 15.5%, and 10.0% of tested patients, respectively. In multivariable analysis, AIDS (odds ratio [OR] 3.31; 95% confidence interval [CI] 1.13-9.64, p = 0.029), non-Hodgkin lymphoma (OR 3.71; 95% CI 1.23-11.18, p = 0.020), vasculitis (OR 5.95; 95% CI 1.07-33.22, p = 0.042), metastatic solid tumor (OR 4.31; 95% CI 1.76-10.53, p = 0.001), and bilateral ground glass on CT scan (OR 2.19; 95% CI 1.01-4.78, p = 0.048) were associated with PJP, whereas an inverse association was observed for increasing lymphocyte cell count (OR 0.64; 95% CI 0.42-1.00, p = 0.049). For the diagnosis of PJP, higher positive predictive value (PPV) was observed when both respiratory Pneumocystis PCR and serum BDG were positive compared to individual assay positivity (72% for the combination vs. 63% for PCR and 39% for BDG). Cumulative 30-day mortality and 90-day mortality in patients with presumptive/proven PJP were 52% and 67%, respectively. CONCLUSION: PJP in critically ill patients admitted to ICU is nowadays most encountered in non-HIV patients. Serum BDG when used in combination with respiratory Pneumocystis PCR could help improve the certainty of PJP diagnosis.

A Community Study of SARS-CoV-2 Detection by RT-PCR in Saliva: A Reliable and Effective Method.

Efficient, wide-scale testing for SARS-CoV-2 is crucial for monitoring the incidence of the infection in the community. The gold standard for COVID-19 diagnosis is the molecular analysis of epithelial secretions from the upper respiratory system captured by nasopharyngeal (NP) or oropharyngeal swabs. Given the ease of collection, saliva has been proposed as a possible substitute to support testing at the population level. Here, we used a novel saliva collection device designed to favour the safe and correct acquisition of the sample, as well as the processivity of the downstream molecular analysis. We tested 1003 nasopharyngeal swabs and paired saliva samples self-collected by individuals recruited at a public drive-through testing facility. An overall moderate concordance (68%) between the two tests was found, with evidence that neither system can diagnose the infection in 100% of the cases. While the two methods performed equally well in symptomatic individuals, their discordance was mainly restricted to samples from convalescent subjects. The saliva test was at least as effective as NP swabs in asymptomatic individuals recruited for contact tracing. Our study describes a testing strategy of self-collected saliva samples, which is reliable for wide-scale COVID-19 screening in the community and is particularly effective for contact tracing.

Parsonage-Turner syndrome following coronavirus disease 2019 immunization with ChAdOx1-S vaccine: a case report and review of the literature.

BACKGROUND: Parsonage-Turner syndrome is an acute peripheral neuropathy that affects the upper brachial plexus region. Previously published reports demonstrate that the condition can be triggered by surgery, infection, autoimmune diseases, strenuous exercise, trauma, radiation, and vaccination. Parsonage-Turner syndrome has already been reported in three other patients who were vaccinated against coronavirus disease 2019. CASE PRESENTATION: We report the case of a 51-year-old Caucasian man without comorbidities who received the first dose of the ChAdOx1-S recombinant vaccine (Vaxzevria, AstraZeneca, Oxford, UK) against coronavirus disease 2019 and was diagnosed with Parsonage-Turner syndrome. A few days after getting vaccinated, the patient reported a progressive increase in pain in the region of vaccine administration. One month later, the shoulder pain was followed by symptoms of hypoesthesia and muscle weakness on abduction and elevation of the left upper limb. Neurological examination revealed an atrophy of the proximal muscles of the left upper limb, accompanied by paresis of the left deltoid, biceps brachii, triceps brachii, and infraspinatus muscles. Electroneuromyography carried out 3 months after the onset of symptoms showed signs consistent with brachial plexus neuritis. The adverse reaction has been properly reported to the Italian Pharmacovigilance System (Italian Medicines Agency-Agenzia Italiana del Farmaco. CONCLUSION: The increased awareness of such association is essential for early identification and diagnosis and, thus, better clinical outcomes.

Current Take on Systemic Sclerosis Patients' Vaccination Recommendations.

Systemic sclerosis (SSc) is a rare autoimmune inflammatory rheumatic disease. The prevalence of SSc ranges from 7 to 700 cases per million worldwide. Due to multiple organ involvement and constant inflammatory state, this group of patients presents an increased risk of infectious diseases. This paper aimed to gather the up-to-date evidence on vaccination strategies for patients with SSc and to be a useful tool for the prevention and management of infectious diseases. The authors conducted a scoping review in which each paragraph presents data on a specific vaccine's safety, immunogenicity, and efficacy. The work deals with the following topics: SARS-CoV-2, seasonal influenza, S. pneumoniae, HAV, HBV, HZV, N. meningitidis, H. influenzae, HPV, and diphtheria-tetanus-pertussis.

Bronchoalveolar lavage fluid characteristics and outcomes of invasively mechanically ventilated patients with COVID-19 pneumonia in Genoa, Italy.

BACKGROUND: The primary objective of the study is to describe the cellular characteristics of bronchoalveolar lavage fluid (BALF) of COVID-19 patients requiring invasive mechanical ventilation; the secondary outcome is to describe BALF findings between survivors vs non-survivors. MATERIALS AND METHODS: Patients positive for SARS-CoV-2 RT PCR, admitted to ICU between March and April 2020 were enrolled. At ICU admission, BALF were analyzed by flow cytometry. Univariate, multivariate and Spearman correlation analyses were performed. RESULTS: Sixty-four patients were enrolled, median age of 64 years (IQR 58-69). The majority cells in the BALF were neutrophils (70%, IQR 37.5-90.5) and macrophages (27%, IQR 7-49) while a minority were lymphocytes, 1%, TCD3+ 92% (IQR 82-95). The ICU mortality was 32.8%. Non-survivors had a significantly older age (p = 0.033) and peripheral lymphocytes (p = 0.012) were lower compared to the survivors. At multivariate analysis the percentage of macrophages in the BALF correlated with poor outcome (OR 1.336, CI95% 1.014-1.759, p = 0.039). CONCLUSIONS: In critically ill patients, BALF cellularity is mainly composed of neutrophils and macrophages. The macrophages percentage in the BALF at ICU admittance correlated with higher ICU mortality. The lack of lymphocytes in BALF could partly explain a reduced anti-viral response.

Determinants of SARS-CoV-2 infection in Italian healthcare workers: a multicenter study.

Healthcare workers (HCWs) are at increased risk of being infected with SARS-CoV-2, yet limited information is available on risk factors of infection. We pooled data on occupational surveillance of 10,654 HCW who were tested for SARS-CoV-2 infection in six Italian centers. Information was available on demographics, job title, department of employment, source of exposure, use of personal protective equipment (PPEs), and COVID-19-related symptoms. We fitted multivariable logistic regression models to calculate odds ratios and 95% confidence intervals of infection. The prevalence of infection ranged from 3.0 to 22.0%, and was correlated with that of the respective areas. Women were at lower risk of infection compared to men. Fever, cough, dyspnea and malaise were the symptoms most strongly associated with infection, together with anosmia and ageusia. No differences in the risk of infection were detected according to job title, or working in a COVID-19 designated department. Reported contact with a patient inside or outside the workplace was a risk factor. Use of a mask was strongly protective against risk of infection as was use of gloves. The use of a mask by the source of exposure (patient or colleague) had an independent effect in reducing infection risk.

Weight of risk factors for mortality and short-term mortality displacement during the COVID-19 pandemic.

Background: We conducted a population-based cohort study to estimate mortality before, during and after the COVID-19 peak and to compare mortality in 2020 with rates reported in previous years, with a view to helping decision makers to apply containment measures for high-risk groups. Methods: All deaths were collected between 2015 and 2020 from municipal registry database. In 2020, weeks 1-26 were stratified in three periods: before, during and after the COVID mortality peak. The Poisson Generalized Linear regression Model showed the "harvesting effect". Three logistic regressions for 8 dependent variables (age and comorbidities) and a t-test of differences described all-cause mortality risk factors in 2019 and 2020 and differences between COVID and non-COVID patients. Results: A total of 47,876 deaths were collected. All-cause deaths increased by 38.5% during the COVID peak and decreased by 18% during the post-peak period in comparison with the average registered during the control period (2015-19), with significant mortality displacement in 2020. Except for chronic renal injuries in subjects aged 45-64 years, diabetes and chronic cardiovascular diseases in those aged 65-84 years, and neuropathies in those aged > 84 years, the weight of comorbidities in deaths was similar or lower in COVID subjects than in non-COVID subjects. Discussions: Surprisingly, the weight of comorbidities in death, compared to weight in non-COVID subjects allows you to highlight some surprising results such as COPD, IBD and Cancer. The excess mortality that we observed in the entire period were modest in comparison with initial estimates during the peak, owing to the mild influenza season and the harvesting effect starting from the second half of May.

Human Papilloma Virus Infection and Vaccination: Pre-Post Intervention Analysis on Knowledge, Attitudes and Willingness to Vaccinate Among Preadolescents Attending Secondary Schools of Palermo, Sicily.

In recent years, vaccination coverage rates against Human Papilloma Virus (HPV) in Europe have shown a decreasing trend and remain below the required standard. The present study aims to assess knowledge and attitudes regarding HPV infection and vaccination among a representative sample of preadolescents of Palermo, Italy. A survey was carried out throughout two questionnaires, before and after carrying out an educational intervention scheduled during school hours. A total of 1702 students attending first-grade secondary schools of the province of Palermo were enrolled (response rate 68.9%). Students attending third classes (adj OR = 1.18; CI 95% 1.03-1.36), being of higher socioeconomic status (adj OR = 1.35; CI 95% 1.05-1.73), who had previously received information about sexually transmitted diseases (STDs) at home (adj OR = 1.62; CI 95% 1.27-2.07) or at school (adj OR = 2.15; CI 95% 1.70-2.71) and who had ever heard in the past about HPV (adj OR = 1.80; CI 95% 1.42-2.29) showed a significantly higher baseline level of knowledge regarding HPV. Willingness to receive HPV vaccination, in a 10-point Likert scale, significantly increased between the pre- (8.51; SD ± 1.79) and post- (9.01 SD ± 1.52) intervention questionnaires (p < 0.001). A total of 188 out of 272 (69.1%) preadolescents attending five out eighteen schools involved in the project, who had not previously received the HPV vaccine, were vaccinated. During past years, education campaigns on HPV were mainly dedicated to adult women, excluding teenagers and omitting young males. It should therefore be of primary importance that school-based education and vaccination programmes be standardized.

Italian Health Care Workers' Knowledge, Attitudes, and Practices Regarding Human Papillomavirus Infection and Prevention.

Objective: To assess healthcare workers' knowledge and attitudes about human papillomavirus (HPV) infection, related diseases, and prevention. Methods: A cross-sectional multicenter survey about HPV and its prevention, targeted to healthcare workers involved in HPV vaccine counseling, was performed from May 2017 to December 2018. Results: The overall median knowledge and attitude scores were 69.2% (25-75, p = 61.5-84.6) and 5 (25-75, p = 4-5), respectively. Both knowledge and attitudes statistically significantly differ between physicians and healthcare professions. The median propensity score before and after the educational intervention was stable and high, at 10 (25-75, p = 9-10). The predictors of statistically significantly high knowledge scores are to be a physician, general practitioner, or pediatrician, attending courses/congresses, and consulting technical product characteristics and scientific literature to obtain information about the HPV vaccine. Being a physician and consulting scientific literature to obtain information about the HPV vaccine were found also as predictors of statistically significantly different attitude scores among study participants. Conclusions: Although healthcare workers showed overall positive attitudes towards the relevance of HPV burden and prevention tools, demonstrated knowledge was largely suboptimal, particularly that shown by healthcare professions. Obtained results allow highlighting knowledge gaps, and thus improving counselling to HPV vaccine targets.

Advances in therapeutic vaccines for treating human papillomavirus-related cervical intraepithelial neoplasia.

AIM: Human papillomavirus (HPV) is the etiologic agent of the majority of cervical intraepithelial lesions (CIN) and cervical cancers. While prophylactic HPV vaccines prevent infections from the main high-risk HPV types associated with cervical cancer, alternative nonsurgical and nonablative therapeutics to treat HPV infection and preinvasive HPV diseases have been experimentally investigated. Therapeutic vaccines are an emerging investigational strategy. This review aims to introduce the results of the main clinical trials on the use of therapeutic vaccines for treating HPV infection and -related CIN, reporting the ongoing studies on this field. METHODS: Data research was conducted using MEDLINE, EMBASE, Web of Sciences, Scopus, ClinicalTrial.gov, OVID and Cochrane Library querying for all articles related to therapeutic vaccines for the treatment of HPV-related CIN. Selection criteria included randomized clinical trials, nonrandomized controlled studies and review articles. RESULTS: Preliminary data are available on the evaluation of therapeutic vaccines for treating cervical HPV infections and CIN. Despite having in vitro demonstrated to obtain humoral and cytotoxic responses, therapeutic vaccines have not yet clinically demonstrated consistent success; moreover, each class of therapeutic vaccines has advantages and limitations. Early clinical data are available in the literature for these compounds, except for MVA E2, which reached the phase III clinical trial status, obtaining positive clinical outcomes. CONCLUSION: Despite promising results, to date many obstacles are still present before hypothesize an introduction in the clinical practice within the next years. Further studies will draw a definitive conclusion on the role of therapeutic vaccines in this setting.

Assessment of Knowledge, Attitudes, and Propensity towards HPV Vaccine of Young Adult Students in Italy.

BACKGROUND: Human Papillomavirus (HPV) is a common sexually transmitted infection (STI), representing the main cause of genital warts and cervical cancer. This cross-sectional study evaluated knowledge and attitudes about HPV infection, related diseases, and prevention and propensity towards HPV vaccine among undergraduate students. METHODS: An online and written survey about HPV and its prevention, targeted to young adults of both genders, was addressed to students attending health sciences and other schools at Universities of Genoa and Bari. RESULTS: The overall median knowledge and attitude scores were 56.3% (25-75 p = 40-68.8%) and four out of five (25-75 p = 4-5), respectively. In the multivariate analysis, attending a health sciences university, using social networks ≤2 h a day, a history of STI, having heard about HPV and HPV vaccine previously resulted as predictors of higher knowledge scores. Having heard about HPV previously also predicted a high attitude score, together with a perceived economic status as good. Having Italian and healthcare worker parents, being employed, and following a specific diet, instead, predicted lower attitude score. CONCLUSIONS: Poor knowledge and good attitudes were found among undergraduates about HPV. In order to increase HPV vaccine compliance and the counselling skills of future healthcare workers, the improvement of training on HPV is needed.

Burden and Prevention of HPV. Knowledge, Practices and Attitude Assessment Among Pre-Adolescents and their Parents in Italy.

Despite infections due to HPV nowadays represent the most common sexually transmitted diseases worldwide with recognized effective and safe preventive strategies, knowledge, attitudes; however, awareness on HPV is considerably low. The present study has two main objectives: 1. To conduct a literature review to analyze the evolution of preventive tools, the complexity of the vaccine choice process, and the challenges posed by HPV vaccine hesitancy and refusal among pre-adolescents and their parents; 2. To assess knowledge, practices and attitudes toward HPV infection and vaccination in a sample of Italian pre-adolescents and their parents. The observational study was carried out through the use of two anonymous and self-administered pre- and postintervention questionnaires dedicated to the target populations. Between the administrations of the pre- and postintervention questionnaires, an educational intervention on HPV infection and related diseases, and prevention strategies was conducted. All participants demonstrated suboptimal knowledge and positive attitudes in the preintervention questionnaire. Higher levels of knowledge and attitudes were observed among pre-adolescents thatused social networks and had heard of sexually transmitted diseases at home/school/physician and from parents and also who had heard of HPV from General Practitioners, Gynecologists, family members and newspapers. A significant increase in HPV vaccination awareness was observed among pre-adolescents after the educational sessions. Health education programs aimed at increasing knowledge, attitudes and awareness on HPV are needed to implement the outcomes of HPV immunization programs, especially if supported by the physicians involved in counselling and recommendation processes.

Hospital and economic burden of influenza-like illness and lower respiratory tract infection in adults ≥50 years-old.

BACKGROUND: Influenza-like illnesses (ILIs) and lower respiratory tract infections (LRTIs) cause substantial morbidity and mortality worldwide. The study assessed the health and economic burden of ILI and LRTI according to age and comorbidities, since available evidence is limited and heterogeneous. METHOD: The prevalence of comorbidities, the seasonal incidence rates and the mean and per capita direct costs of ED accesses for ILI/LRTI, whether followed by hospitalization or not, recorded in adults aged ≥50 years over the last 6 years, in the referral hospitals located in the Genoese metropolitan area (Liguria, Italy) where the syndromic surveillance system is active, were evaluated through a retrospective observational study. Comorbidities were estimated through the Chronic Condition Data Warehouse that integrates multiple Medicare data sources. A comparison with the administrative healthcare International Classification of Diseases-9th revision-Clinical Modification (ICD-9-CM)-based data was also conducted. RESULTS: The prevalence of subjects with ≥1 comorbidity ranged from 23.49 to 59.92%. The most prevalent all-age comorbidities were cardiovascular diseases and cancer. The overall ILI/LRTI incidence rate was 6.73/1000 person-years, almost double the value derived from routine data, and increased with age. The highest rates were observed in patients with renal failure and bronchopneumopathies. The mean cost of ED accesses/hospitalization for ILI/LRTI was €3353 and was almost twice as high in the ≥85 years as in the youngest age-group. The highest mean costs were observed in patients with renal failure and cancer. The per capita costs increased from €4 to €71 with age, and were highest in patients with renal failure and bronchopneumopathy. CONCLUSION: The burden of ILIs/LRTIs in terms of ED accesses and hospitalizations in adults aged ≥50 years is heavy, and is related to increasing age and, especially, to specific comorbidities. These results could contribute to revising age- and risk-based anti-influenza and -pneumococcus immunization strategies.

Immunization Campaigns and Strategies against Human Papillomavirus in Italy: The Results of a Survey to Regional and Local Health Units Representatives.

Objective. The study aimed to assess the impact of HPV immunization campaigns organizational aspects, the characteristics of immunization program (vaccination targets and type of offer), and communicative strategies adopted by four Italian administrative regions on vaccination coverage observed. Methods. From November 2017 to March 2018, regional and Local Health Units (LHUs) representatives were invited to complete an online survey including 54 questions evaluating vaccination invite systems, access systems to vaccination centres, reminder and recall systems, and adverse events surveillance. An overall descriptive analysis was conducted. Since observed vaccine coverage (VC) obtained in females (2002-2004 birth cohorts) was lower than objectives fixed by the Italian Ministry of Health, variables were assessed using the national VC mean obtained in the 2003 girls birth cohort as outcome. Results. Twenty-six LHUs belonging to 4 Northern and Southern Italian regions participated in the study. Organizational aspects significantly related to VC lower than the national mean were access to vaccine centres without appointment and parents' reservation as appointment planning system. Recall systems for both the first and the second dose, including the appointment in the invitation letter, the availability of regional immunization registry, and education of healthcare workers on universal HPV immunization strategies, instead, were related to higher VC. As regards preadolescent immunization strategies, both VC obtained in girls and boys were far from the Ministerial goals. Only 20% of LHUs introduced multicohort female strategies while all LHUs adopted copayment targeting both men and women. Immunizations strategies targeting subjects at risk were implemented only in half of participating LHUs. Conclusions. VC observed in participating LHUs are largely lower than the national objectives in all anti-HPV vaccine targets. Both organizational and educational strategies have to be implemented to improve the VC goals.

Universal influenza virus vaccines: what needs to happen next?

INTRODUCTION: Influenza occurs worldwide and causes significant disease burden in terms of morbidity, associated complications, hospitalizations, and deaths. Vaccination constitutes the primary approach for controlling influenza. Current influenza vaccines elicit a strain-specific response yet occasionally exhibit suboptimal effectiveness. This review describes the limits of available immunization tools and the future prospects and potentiality of universal influenza vaccines. AREAS COVERED: New 'universal' vaccines, which are presently under development, are expected to overcome the problems related to the high variability of influenza viruses, such as the need for seasonal vaccine updates and re-vaccination. Here, we explore vaccines based on the highly conserved epitopes of the HA, NA, or extracellular domain of the influenza M2 protein, along with those based on the internal proteins such as NP and M1. EXPERT OPINION: The development of a universal influenza vaccine that confers protection against homologous, drifted, and shifted influenza virus strains could obviate the need for annual reformulation and mitigate disease burden. The scientific community has long been awaiting the advent of universal influenza vaccines; these are currently under development in laboratories worldwide. If such vaccines are immunogenic, efficacious, and able to confer long-lasting immunity, they might be integrated with or supplant traditional influenza vaccines.

Overview of hepatitis B virus mutations and their implications in the management of infection.

Hepatitis B virus (HBV) affects approximately two billion people worldwide and more than 240 million people in the world are currently chronic carrier that could develop serious complications in the future, like liver cirrhosis and hepatocellular carcinoma. Although an extended HBV immunization program is being carried out since the early '80s, representing effective preventive measure, leading to a dramatic reduction of HBV hepatitis incidence, globally HBV infection still represents a major public health problem. The HBV virus is a DNA virus belongs to the Hepadnaviridae family. The HBV-DNA is a circular, partial double strand genome. All coding information is on the minus DNA strand and it is organized into four open reading frames. Despite hepatitis B virus is a DNA virus, it has a high mutation rate due to its replicative strategy, that leads to the production of many non-identical variants at each cycle of replication. In fact, it contains a polymerase without the proofreading activity, and uses an RNA intermediate (pgRNA) during its replication, so error frequencies are comparable to those seen in retroviruses and other RNA viruses rather than in more stable DNA viruses. Due to the low fidelity of the polymerase, the high replication rate and the overlapping reading frames, mutations occur throughout the genome and they have been identified both in the structural and not structural gene. The arise of mutations being to develop of a whole of viral variants called "quasi-species" and the prevalent population, which favors virus replication, was selected by viral fitness, host's immune pressure and external pressure, i.e., vaccination or antiviral therapy. Naturally occurring mutations were found both in acute and chronic subjects. In the present review we examine and discuss the most recent available data about HBV genetic variability and its significance.