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Coronavirus disease 19 (COVID-19) is clinically less severe in children, even if the wide variety and degree of severity of symptoms reported in children pose a still-unresolved challenge for clinicians. We performed an in-depth analysis of the immunological profiles of 18 hospitalized SARS-CoV-2-infected children, whose results were compared to those obtained from 13 age- and sex-matched healthy controls (HC). The patients were categorized as paucisymptomatic/moderate (55.6%) or severe/critical (44.5%) according to established diagnostic criteria and further stratified into the categories of infants (1–12 months), children (1–12 years), and adolescents (>12 years). We assessed SARS-CoV-2-specific RBD antibodies (Ab), neutralizing antibodies (nAb), and circulating cytokines/chemokines in the plasma, and the SARS-CoV-2-specific immune response was measured in PBMCs by gene expression and secretome analyses. Our results showed peculiar circulating cytokine/chemokine profiles among patients sharing a similar clinical phenotype. A cluster of patients consisting of infants with severe symptoms presented hyperinflammatory profiles, together with extremely polarized antibody profiles. In a second cluster consisting of paucisymptomatic patients, a less pronounced increase in the level of inflammatory cytokines, together with an association between the selected cytokines and humoral responses, was observed. A third cluster, again consisting of paucisymptomatic patients, showed a circulating cytokine/chemokine profile which overlapped with that of the HC. The SARS-CoV-2-stimulated production of pro-inflammatory proteins, T lymphocyte activation, and migration-specific proteins, were significantly increased in SARS-CoV-2-infected children compared to the HC. Our findings suggest that immune response activation in the course of SARS-CoV-2 infection in children is directly correlated with clinical severity and, to a lesser extent, age.

Despite the COVID-19 pandemic, influenza remains an important issue. Especially in community settings, influenza outbreaks can be difficult to control and can result in high attack rates. In April 2022, a large A(H3N2) influenza outbreak spread in the largest Italian drug-rehabilitation community. One hundred eighty-four individuals presented influenza-like symptoms (attack rate of 26.2%); 56% previously received the influenza vaccine. Sequence analyses highlighted a genetic drift from the vaccine strain, which may have caused the observed lack of protection.

Improving influenza vaccination coverage in young children is crucial in reducing the spreading of influenza viruses, thus indirectly protecting the general population. Mass campaign needs to engage all the communities within the target population, overcoming socio-economic and cultural barriers. School-located interventions in some countries were successful in increasing vaccine acceptability and overall immunisation rates.Influenza-like illnesses (ILI) share several symptoms with the ongoing COVID-19 pandemic, posing an important challenge for both diagnostics and public health burden. Self-sampling using non-invasive saliva collection could represent a suitable tool for respiratory infection surveillance.This pilot study was carried out in a very densely populated Italian area, Milan, characterised by a high percentage of non-Italian citizens, often hard-to-reach by preventive programmes. We started a vaccine campaign with live-attenuated influenza vaccine (LAIV), recently recommended in Italy for children aged 2-6, coupled with a saliva-based ILI surveillance system in preschools.We enrolled 432 children from 5 schools in the Milan suburbs, 31.2% of which received the LAIV. Thanks to the undertaken multicultural approach, 59% of the vaccinated children were non-Italian citizens.Despite the COVID-19 preventive measures, i.e., school closure upon positive cases, highly affected the programmed surveillance, all the saliva samples from ILI cases, self-collected by parents at home, resulted adequate for viral molecular testing.With correction measures, this pilot experience could be broadened to a large population, simultaneously allowing for a widespread ILI surveillance and flu immunisation.

Measles is one of the most contagious diseases known to man. Despite the existence of a safe and effective live attenuated vaccine, measles can appear in vaccinated individuals. Paradoxically, breakthrough cases increase as vaccination coverage in the general population rises. In measles endemic areas, breakthrough cases represent less than 10% of total infections, while in areas with high vaccination coverage these are over 10% of the total. Two different vaccination failures have been described: primary vaccination failure, which consists in the complete absence of humoral response and occurs in around 5% of vaccinated individuals; and secondary vaccination failure is due to waning immunity or incomplete immunity and occurs in 2-10% of vaccinees. Vaccination failures are generally associated with lower viral loads and milder disease (modified measles) since vaccination limits the risk of complicated disease. Vaccination failure seems to occur between six and twenty-six years after the last vaccine dose administration. This review summarizes the literature about clinical, serological, epidemiological, and molecular characteristics of measles breakthrough cases and their contribution to virus transmission. In view of the measles elimination goal, the assessment of the potential decline in antibody protection and the targeted implementation of catch-up vaccination are essential.

During the COVID-19 public health emergency, an increasing number of studies reported the occurrence of SARS-CoV-2 in wastewaters worldwide, but little is known about the presence of the virus in surface freshwaters. The aim of the current study was to develop and validate an appropriate and scalable methodological approach for the concentration and detection of SARS-CoV-2 from surface freshwater samples, collected within the Milan rural network subjected to flood spillways activity. Overall, both surface water and distilled water samples spiked with inactivated SARS-CoV-2 were used to validate the concentration method for pathogens determination. Two pre-filtration systems, filter paper and Sartolab® P20 (Sartorius, Germany) and two concentration methods, two-phase (PEG-dextran method) separation and tangential flow ultrafiltration (UF), were compared. The effects of pre-filtration and concentration on viral nucleic acid recovery were assessed through real time RT-PCR targeting SARS-CoV-2 and the internal viral control PMMoV (Pepper Mild Mottle Virus). Our results showed that UF is more sensitive than the PEG-dextran method in viral acid nucleic recovery from surface water samples. Better results were obtained pre-filtering samples with Sartolab® P20 and extracting the nucleic acids with undiluted silica, rather than diluted as required by the standard protocol. The proposed method will be used for the monitoring of surface waters in the Milan area.

Two years after the start of the COVID-19 pandemic, key questions about the emergence of its aetiological agent (SARS-CoV-2) remain a matter of considerable debate. Identifying when SARS-CoV-2 began spreading among people is one of those questions. Although the current canonically accepted timeline hypothesises viral emergence in Wuhan, China, in November or December 2019, a growing body of diverse studies provides evidence that the virus may have been spreading worldwide weeks, or even months, prior to that time. However, the hypothesis of earlier SARS-CoV-2 circulation is often dismissed with prejudicial scepticism and experimental studies pointing to early origins are frequently and speculatively attributed to false-positive tests. In this paper, we critically review current evidence that SARS-CoV-2 had been circulating prior to December of 2019, and emphasise how, despite some scientific limitations, this hypothesis should no longer be ignored and considered sufficient to warrant further larger-scale studies to determine its veracity.

Il "progetto Michelangelo" è nato dall'esigenza di rallentare la diffusione dei contagi da SARS-CoV-2 e alleggerire il carico a livello ospedaliero. Inizialmente, la maggior parte degli ospiti dell'hotel Michelangelo di Milano erano pazienti dimessi dagli ospedali con test molecolare ancora positivo che non avevano la possibilità di restare in isolamento domiciliare. Ben presto, però, il progetto è stato esteso e circa un ospite su quattro era un adulto/nucleo familiare in condizioni di grave disagio economico o sociale o una persona senza fissa dimora. Inoltre, la maggior parte degli ospiti era di nazionalità non italiana: persone che, a causa di barriere linguistiche, legali, culturali e sociali, hanno trovato maggiore difficoltà ad avere un rapido accesso ai servizi sanitari. Il "progetto Michelangelo" non ha solo contribuito a ridurre il sovraffollamento degli ospedali, ma è stato di supporto ai servizi rivolti al contrasto della grave marginalità.

We identified severe acute respiratory syndrome coronavirus 2 RNA in an oropharyngeal swab specimen collected from a child with suspected measles in early December 2019, ≈3 months before the first identified coronavirus disease case in Italy. This finding expands our knowledge on timing and mapping of novel coronavirus transmission pathways.

Zika virus (ZIKV), a vector-borne infectious agent that has recently been associated with neurological diseases and congenital microcephaly, was first reported in the Western hemisphere in early 2015. A number of authors have reconstructed its epidemiological history using advanced phylogenetic approaches, and the majority of Zika phylogeography studies have used discrete diffusion models. Continuous space diffusion models make it possible to infer the possible origin of the virus in real space by reconstructing its ancestral location on the basis of geographical coordinates deduced from the latitude and longitude of the sampling locations. We analysed all the ZIKV complete genome isolates whose sampling times and localities were available in public databases at the time the study began, using a Bayesian approach for discrete and continuous phylogeographic reconstruction. The discrete phylogeographic analysis suggested that ZIKV emerged to become endemic/epidemic in the first decade of the 1900s in the Ugandan rainforests, and then reached Western Africa and Asia between the 1930s and 1950s. After a long period of about 40 years, it spread to the Pacific islands and reached Brazil from French Polynesia. Continuous phylogeography of the American epidemic showed that the virus entered in north-eastern Brazil in late 2012 and started to spread in early 2013 from two high probability regions: one corresponding to the entire north-east Brazil and the second surrounding the city of Rio de Janeiro, in a mainly northwesterly direction to Central America, the north-western countries of south America and the Caribbean islands. Our data suggest its cryptic circulation in both French Polynesia and Brazil, thus raising questions about the mechanisms underlying its undetected persistence in the absence of a known animal reservoir, and underline the importance of continuous diffusion models in making more reliable phylogeographic reconstructions of emerging viruses.

The benefits of schools’ closure, used as a containment strategy by many European countries, must be carefully considered against the adverse effects of child wellbeing. In this study, we assessed SARS-CoV-2 seroprevalence, which better estimates the real extent of the infection unraveling asymptomatic cases, among schoolchildren aged 3 to 18 in Milan, using dried blood spot, a safe and extremely viable methods for children, and then compared it between September 2020 and January 2021. Secondly, we evaluated the seroconversion rate and compared it between students attending schools in presence and those switched to distance-learning, using a logistic regression model, both as univariate and multivariate, adjusting for age and biological-sex. Among 1109 pupils, we found a seroprevalence of 2.8% in September before school reopening, while in January 2021, the seropositive rate was 12.5%, reflecting the general growth rate of infections during the second pandemic wave. The overall seroconversion rate was 10%, with no differences based on biological-sex and age groups; we observed no seroreversion. When considered age groups, the seroconversion rate was 10.5% (95%Confidence Interval, 2.9–24.8) among children attending preschools, 10.6% (95%Confidence Interval, 8.2–13.4) for primary schools, 9.9% (95%Confidence Interval, 6.8–13.8) for secondary schools, and 7.8% (95%Confidence Interval, 4–13.2) among high-school students. Interestingly, no differences in seroconversion rate were found between students who attended school compared to those who started remote learning in the first days of November. Furthermore, most patients (61%) reported that the contact occurred within the household. We reported a low seroconversion rate among school children in Milan, with no differences between those who attended from September 2020 to January 2021 compared to those who switched to remote learning in the first days of November. Our data suggest that schools do not amplify SARS-CoV-2 transmission, but rather reflect the level of the transmission in the community.

Background: Skin manifestations have been reported in patients with SARS-CoV-2 infection. As a reference laboratory for measles and rubella surveillance in Lombardy, we evaluated the association between SARS-CoV-2 infection and measles-like symptomatology while providing evidence for undetected early circulation of SARS-CoV-2. Methods: Overall, 435 samples from 156 cases were investigated. RNA isolated from oropharyngeal swabs (N=148) and urine (N=141) was screened by hemi-nested PCRs targeting key sites for viral typing. After Sanger sequencing, detected mutations were used to estimate the time of emergence of the progenitor SARS-CoV-2 using a previously calibrated molecular clock. Sera (N=146) were tested for anti-SARS-CoV-2 IgG, IgM, and IgA, and the titre of neutralizing antibodies was assessed. Findings: Molecular evidence for SARS-CoV-2 infection was found in 13 subjects. Two patients were from the pandemic period (2/12, 16·7%, March 2020-March 2021) and 11 were from the pre-pandemic period (11/44, 25%, August 2019-February 2020). Five of the positive individuals showed the simultaneous presence of anti-SARS-CoV-2 antibodies. No clear evidence of infection was found in 281 samples collected between August 2018 and July 2019 from 100 patients. The first positivity for SARS-CoV-2 RNA was found in a sample collected on September 12, 2019. Mutations typical of B.1 (PANGOLIN classification) strains, previously reported to have emerged in January 2020, had already been circulating in October 2019. Hence, we estimate SARS-CoV-2 progenitor of known human infections to have emerged in late June-late August 2019. Interpretations: We find evidence that SARS-CoV-2 was circulating in Lombardy during the late summer of 2019. This finding highlights the importance of retrospective surveillance studies to understand the early dynamics of COVID-19 spread and improve national-level preparedness. Funding Information: Research support from: Romeo and Enrica Invernizzi Pediatric Research Center, University of Milan, Milan, Italy; U.S. National Science Foundation to S.K. and S.M. (DEB‐2034228) and S.P. (DBI‐2027196); U.S. National Institutes of Health to S.K. (GM‐139504) and S.P. (AI‐134384 Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: This work was carried out as part of the Integrated Measles-Rubella Surveillance, performed by law in accordance with the Prime Minister's Decree of 3 March 2017 (https://www.gazzettaufficiale.it/eli/id/2017/05/12/17A03142/sg). The retrospective study was conducted in the absence of consent following the declaration of state of emergency caused by the SARS-CoV-2 pandemic, in accordance with letter i, article 9 of the GDPR (https://eurlex.europa.eu/legal-content/IT/TXT/HTML/?uri=OJ:L:2016:119:FULL&from=FI).

Serological surveillance is necessary to the reestablishment of school activities in safe conditions and to avoid school-related outbreaks. In this study, DBS (Dried Blood Spots) have proven to be a simple, rapid and reliable sample collection tool for detecting antibodies against SARS-CoV-2 by ELISA test compared to matched serum samples from venous sampling (R2=0.9553; Pearson’s coefficient=0.98; Cohen’s unweighted k=0.93; overall agreement=96.2%). This approach may facilitate sample collection from schoolchildren for serological surveys useful to an adequate risk-assessment.

Of the 24 known measles genotypes, only D8 and B3 are responsible for outbreaks in the last years in Europe, Asia, and America. In this study the H gene of 92 strains circulating between 2015 and 2019 in Lombardy, Northern Italy, and 1273 H sequences available in GenBank were analyzed in order to evaluate the genetic variability and to assess the conservation of the immunodominant sites. Overall, in Lombardy we observed the presence of four different B3 and three different D8 clusters, each one of them including sequences derived from viruses found in both vaccinated and unvaccinated subjects. Worldwide, the residue 400 within the H protein, a position located within the main immune epitope, is mutated in all circulating strains that belong to the two globally endemic genotypes, B3 and D8. Our data demonstrate the usefulness of measles virus (MV) H gene sequencing. Indeed, the monitoring the H protein epitopes of circulating strains could be included in the measles laboratory surveillance activities in order to improve and optimize strategies for measles control, as countries go towards elimination phase.

Viral factors, such as high‑risk human papillomavirus variants, can increase the risk of viral persistence and influence the progression to cancer. In the present study, the long control region (LCR) of human papillomavirus (HPV)‑16 and HPV‑52, and the L1 region of HPV‑16 and HPV‑18, identified from subjects belonging to both general and high‑risk populations (migrants, HIV+ subjects and adolescent/young people) residing in Italy, were characterized using molecular and phylogenetic techniques. To the best of our knowledge, this is the first Italian study to analyze a large number of sequences (n=458) and report phylogenetic data on the HPV‑52 variants. The phylogenetic analysis showed that 90% of the LCR variants of HPV‑16 and HPV‑52 clustered within lineage A (European lineage) and only sequences identified from subjects belonging to high‑risk populations fell into the non‑European lineages. Analysis of the LCRs revealed a high genomic diversity with a large number of changes. Several mutations in the binding sites for viral and cellular transcription factors characterized the HPV‑16 LCR variants belonging to the African lineages B and C, were observed in subjects with cytological abnormalities (high squamous intraepithelial lesions). The HPV‑16 and HPV‑18 L1 molecular characterization identified 30% of changes in the immune‑dominant epitope loops. These data give a clear picture of the situation in Italy, and a starting point for understanding the molecular pathogenesis and developing molecular diagnostics for HPV, vaccines and other therapeutic approaches in order to control and/or eliminate virus‑induced diseases.

Sequencing the whole measles virus hemagglutinin (H) gene, in conjunction with a 450-nucleotide region of the nucleoprotein gene (N-450), is helpful for the identification of new genotypes and as an auxiliary in outbreak characterization. In addition, it is essential to be able to predict the antigenic changes of the H protein to gain a better monitoring of the response to the vaccine. In this study, we obtained the full-length H gene sequences from 19 measles virus (MV) strains belonging to two B3 genotype variants circulating in Lombardy (Northern Italy) between July 2015 and February 2016 and evaluated the variability of the whole MV-H gene. Furthermore, we compared the obtained H amino acid sequences to all MV sequences available in the GenBank database (n = 1152 in total) and analyzed the amino acid substitutions in the H protein within clades where the Italian strains were included. We identified a higher variability in the H gene compared to the N-450 region and our results support previous studies, highlighting that the H gene is more informative for characterizing the MV B3 genotype than the N-450 sequence. Some of the amino acid substitutions were fixed in the viral population and, remarkably, some of the amino acid substitutions were typically present only in the Italian sequences. Accumulating further molecular information about MV-H gene will be necessary to enable in-depth analyses of the variability of this gene in the vaccinated population.

In 2017, Italy experienced a large measles epidemic with 5408 cases and four deaths. As Subnational Reference Laboratory of the Measles and Rubella surveillance NETwork (MoRoNET), the EpiSoMI (Epidemiology and Molecular Surveillance of Infections) Laboratory (University of Milan) set up rapid and active surveillance for the complete characterisation of the Measles virus (Mv) responsible for the large measles outbreak in Milan and surrounding areas (Lombardy, Northern Italy). The aims of this study were to describe the genetic profile of circulating viruses and to track the pathway of measles transmission. Molecular analysis was performed by sequencing the highly variable 450 nucleotides region of the N gene (N-450) of Mv genome. Two-hundred and ninety-nine strains of Mv were analysed. The phylogenetic analysis showed five different variants, two not previously described in the studied area, belonging to D8 and B3 genotypes. Three events of continuous transmission of autochthonous variants (D8-Osaka, D8-London and B3-Milan variants) and two events of continuous transmission of imported variants (B3-Dublin and D8-Hulu Langat) tracked five different transmission pathways. These pathways outlined two epidemic peaks: the first in April and the second in July 2017. The correlation between Mv variant and the epidemiological data may enable us to identify the sources of virus importation and recognise long-lasting virus transmission pathways.

This study aims to describe and characterize incident HR-HPV infections and associated diseases in HIV-infected women. 805 HIV-infected women enrolled in the VALHIDATE Study were screened and followed-up for HPV by co-testing. Social, behavioral and health data were collected. HPV-DNA positive samples were typed using a commercial kit or RFLP analysis. Conventional Pap-smears were evaluated using the 2001 Bethesda System. The participants with abnormal cytological results were referred for colposcopy. 565 HIV-infected women (median age: 43 years) were analysed, 40.9% had >5 lifetime sexual partners, 77.2% contracted HIV through sexual intercourse, 93% were receiving antiretroviral treatment and 77.3% had undetectable HIV-RNA. The women underwent 1254 follow-ups (median follow-up: 33 months) for 1430.6 PersonYear-Follow-Up. 37.4% of baseline HPV-negative women acquired incident HPV-infections, 69.6% of which were HR-HPVs. HPV-53 was the most common HPV type detected (9.3%). 18.2% of women showed incident or progressive cytological abnormalities (7.8% ASC-US, 9.7% LSIL and 0.6% HSIL) and colposcopy revealed CIN2 (N = 2), CIN1 (N = 2) and VIN3 (N = 1). The preventable fraction of incident infections was 11.3%, 16.7%, and 35.2% for the 2v-4v-9v-HPV vaccines respectively (χ2 p

Human papillomavirus infection is a cause of the development of invasive cervical cancer. Three types of vaccine are currently available to prevent precancerous/cancerous lesions due to persistent infection, which is supported mainly by 7 different high-risk genotypes. The aim of this pilot study was to acquire preliminary data on type-specific prevalence 10 years after the implementation of the HPV vaccination program in Italy, in order to subsequently plan appropriate observational studies in the Italian population. First-voided urine samples were collected from 393 consenting subjects, both females and males, aged 18–40 years, and HPV DNA was detected by PCR amplification of a 450 bp L1 fragment. All amplified products were genotyped by means of the Restriction Fragment Length Polymorphism (RFLP) method. The female population was divided into three cohorts (“vaccine-eligible”, “pre-screening” and “screening” cohorts) according to the preventive intervention scheduled by age; males were included in the same three cohorts according to their year of birth. The overall prevalence of HPV infection was 19%, being higher in females than in males (22.1% vs. 13.6%, p = 0.03729). In the female population, 10 years after the start of the national immunization program, we observed a reduction in the prevalence of vaccine types and the number of circulating genotypes, especially in the “vaccine-eligible” cohort. The frequency of HPV vaccine types increased with age, particularly in males in the “pre-screening” and “screening” cohorts. Our study highlights the importance of monitoring HPV infection in both genders, to validate the effect of the HPV vaccination program.

In 2013, the majority of the WHO/EUR countries reported an annual incidence of >1 case per one million population indicating that the elimination target is far from being met. Thus, there is the urgent need to uncover and analyze chains of measles virus (MV) transmission with the objective to identify vulnerable groups and avoid possible routes of introduction of MV variants in the European population. The analysis of molecular epidemiology of MV B3 strains identified in 2014 has shown that four different variants co-circulated in Italy, including the strain that caused a cruise-line ship outbreak at the beginning of the year.

A large measles outbreak has been ongoing in Milan and surrounding areas. From 1 March to 30 June 2017, 203 measles cases were laboratory-confirmed (108 sporadic cases and 95 related to 47 clusters). Phylogenetic analysis revealed the co-circulation of two different genotypes, D8 and B3. Both genotypes caused nosocomial clusters in two hospitals. The rapid analysis of epidemiological and phylogenetic data allowed effective surveillance and tracking of transmission pathways.

In accordance with the goal of the World Health Organization Regional Office for Europe, the Italian National Measles and Rubella Elimination Plan aimed to interrupt indigenous measles transmission in Italy by the end of 2015. However, from 2013 to 2015, Italy experienced high measles burden with 4902 measles cases (49.3% laboratory-confirmed) reported to the enhanced measles surveillance system (cumulative incidence in the triennium reference period: 2.4/100,000 population). The measles elimination goal was not reached. Laboratory surveillance of measles circulating genotypes is performed by the Measles and Rubella National Reference Laboratory (NRL) at the Italian National Institute of Health (Istituto Superiore di Sanità - ISS), in Rome. Samples received from 1 January 2013-31 December 2015 were analysed. Those positive for measles genome by molecular tests were sequenced and phylogenetically analysed. Phylogenetic analysis performed by NRL identified that genotypes D4 and D8 were endemic and co-circulated in 2011-2013: study results show that genotype D4 disappeared during 2013. Sporadic cases were associated to genotype B3 during 2011-2013, which became endemic in Italy during 2014 and co-circulated with D8 until 2015. Sporadic cases were found belonging to genotypes D9 and H1 all over the period in exam. Similar trend has been observed in European WHO Region.

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in infants and young children. RSV is characterised by high variability, especially in the G glycoprotein, which may play a significant role in RSV pathogenicity by allowing immune evasion. To reconstruct the origin and phylodynamic history of RSV, we evaluated the genetic diversity and evolutionary dynamics of RSV A and RSV B isolated from children under 3 years old infected in Italy from 2006 to 2012. Phylogenetic analysis revealed that most of the RSV A sequences clustered with the NA1 genotype, and RSV B sequences were included in the Buenos Aires genotype. The mean evolutionary rates for RSV A and RSV B were estimated to be 2.1×10-3 substitutions (subs)/site/year and 3.03×10-3 subs/site/year, respectively. The time of most recent common ancestor for the tree root went back to the 1940s (95% highest posterior density-HPD: 1927-1951) for RSV A and the 1950s (95%HPD: 1951-1960) for RSV B. The RSV A Bayesian skyline plot (BSP) showed a decrease in transmission events ending in about 2005, when a sharp growth restored the original viral population size. RSV B BSP showed a similar trend. Site-specific selection analysis identified 10 codons under positive selection in RSV A sequences and only one site in RSV B sequences. Although RSV remains difficult to control due to its antigenic diversity, it is important to monitor changes in its coding sequences, to permit the identification of future epidemic strains and to implement vaccine and therapy strategies. © 2014 Elsevier B.V

The molecular characterization of circulating influenza A viruses is crucial to detect mutations potentially involved in increased virulence, drug resistance and immune escape. A molecular and phylogenetic analysis of A(H1N1)pdm09 neuraminidase (NA) gene sequences from different patient categories defined according to the severity of influenza infection were analyzed. A total of 126 influenza A(H1N1)pdm09 positive samples from patients with severe infections in comparison with those with moderate and mild infections was performed in Lombardy (Northern Italy, nearly 10 million inhabitants) during the 2010–2011 season. NA sequences included in this study segregated into five distinct clusters. Nineteen amino acid substitutions were detected exclusively in NA sequences of viruses identified in patients with severe or moderate influenza infection. Three of them (F74S, S79P, E287K) were observed in virus strains with the 222G/N hemagglutinin mutation. None of NA sequences under study had mutations related to the resistance to the NA inhibitors. Four out of 126 (3.2%) NA sequences from patients with severe infection lost a N-linked glycosylation site due to the change from N to K at residue 386. Two additional N-linked glycosylation sites in the NA stalk region (residues 42 and 44) were found in 12 (9.5%) NA sequences. Sporadic NA mutations were detected in NA viral sequences from critically ill patients, and no variants with reduced sensitivity to NA inhibitors were observed either in treated or untreated patients. J. Med. Virol. 85: 944–952, 2013. © 2013 Wiley Periodicals, Inc.