Longitudinal study of influenza molecular viral shedding in Hutterite communities

The role of asymptomatic infections in influenza transmission: what do we really know

Before the COVID-19 pandemic, the role of asymptomatic influenza virus infections in influenza transmission was uncertain. However, the importance of asymptomatic infection with SARS-CoV-2 for onward transmission of COVID-19 has led experts to question whether the role of asymptomatic influenza virus infections in transmission had been underappreciated. We discuss the existing evidence on the frequency of asymptomatic influenza virus infections, the extent to which they contribute to infection transmission, and remaining knowledge gaps. We propose priority areas for further evaluation, study designs, and case definitions to address existing knowledge gaps.

ADLM Guidance Document on Laboratory Diagnosis of Respiratory Viruses

Respiratory viral infections are among the most frequent infections experienced worldwide. The COVID-19 pandemic has highlighted the need for testing and currently several tests are available for the detection of a wide range of viruses. These tests vary widely in terms of the number of viral pathogens included, viral markers targeted, regulatory status, and turnaround time to results, as well as their analytical and clinical performance. Given these many variables, selection and interpretation of testing requires thoughtful consideration. The current guidance document is the authors' expert opinion based on the preponderance of available evidence to address key questions related to best practices for laboratory diagnosis of respiratory viral infections including who to test, when to test, and what tests to use. An algorithm is proposed to help laboratories decide on the most appropriate tests to use for the diagnosis of respiratory viral infections.

Block the Spread: Barriers to Transmission of Influenza Viruses

Respiratory viruses, such as influenza viruses, cause significant morbidity and mortality worldwide through seasonal epidemics and sporadic pandemics. Influenza viruses transmit through multiple modes including contact (either direct or through a contaminated surface) and inhalation of expelled aerosols. Successful human to human transmission requires an infected donor who expels virus into the environment, a susceptible recipient, and persistence of the expelled virus within the environment. The relative efficiency of each mode can be altered by viral features, environmental parameters, donor and recipient host characteristics, and viral persistence. Interventions to mitigate transmission of influenza viruses can target any of these factors. In this review, we discuss many aspects of influenza virus transmission, including the systems to study it, as well as the impact of natural barriers and various nonpharmaceutical and pharmaceutical interventions.

Knowledge and Attitudes of Healthcare Professionals Regarding Perinatal Influenza Vaccination during the COVID-19 Pandemic

Immunizations during pregnancy are an important aspect of perinatal care. Although the influenza vaccine during pregnancy is safe, vaccination rates are low. According to research data, one of the reasons for the low vaccination rates among pregnant women is that they do not receive a clear recommendation from healthcare providers. This study aims to record the knowledge and attitudes about influenza vaccination and investigate healthcare professionals' recommendations during the perinatal period. A cross-sectional study was conducted with convenience sampling in Athens, Greece. Our purposive sample included 240 midwives, Ob/Gs, and pediatricians. Data were collected using an appropriate standardized questionnaire with information about demographics, attitudes towards influenza vaccination, and knowledge about the influenza virus and peripartum vaccination. Statistical analysis was conducted using IBM SPSS-Statistics version 26.0. This study identifies the reasons for the lack of vaccine uptake including a wide range of misconceptions or lack of knowledge about influenza infection, lack of convenient access to get vaccinated, etc. Misconceptions about influenza and influenza vaccines could be improved by better education of healthcare workers. Continuing professional education for health professionals is necessary to improve the level of knowledge, prevent negative beliefs, and promote preventive and therapeutic practices.

Incidence of Influenza Virus Infection among Wroclaw's Healthcare Workers in Pre-COVID-19 2019-2020 Influenza Season Using Novel Flu SensDx Device

Background: Healthcare workers (HCWs) are more exposed to influenza infection, and the influenza vaccination is recommended each year, to reduce the risk of influenza infection and prevent influenza transmission. This study is a cross-sectional study and the objectives were to determine the rate of influenza virus infection among HCWs in the 2019−2020 influenza season. Methods: Between January and March 2020, a survey was carried out in 2 hospitals and 15 primary health-care settings (PHCS) in Wroclaw (Poland). The novel point-of-care testing Flu SensDx device was used, which detects the M1 protein of the influenza virus using electrochemical impedance spectroscopy from biological material (throat/nasal swabs). Results: A total of 150 samples were collected. The majority of participating HCWs by profession were 83 physicians (55.3%) and half (51.3%) of the participating HCWs worked in PHCS. Influenza vaccination coverage was 61.3% in 2019−2020 and 46.0% in the 2018−2019 season for all participants. Of the participating HCWs, 44.0% were positive tested by the Flu SensDx device. There were no statistically significant differences among the positive tested HCWs, their influenza immunization history, and the presence of symptoms of influenza-like illness (p > 0.05). Conclusion: Although the results of the present study suggest that influenza vaccination does not reduce the frequency of influenza virus detection by Flu SensDx testing in the HCWs participants, larger studies are needed to estimate the incidence of influenza virus infection among HCWs to understand the underlying mechanism and fine-tune policies aimed at reducing nosocomial infections.

Awareness, Attitude, and Current Practices Toward Influenza Vaccination Among Physicians in India: A Multicenter, Cross-Sectional Study

Background: Although annual influenza vaccination is recommended for healthcare providers (HCPs), vaccination rate among HCPs in India is generally low. This cross-sectional survey was conducted to evaluate physicians' awareness, attitude, and current practices toward influenza vaccination in high-risk groups in India.

Methods: The survey was performed in June–July 2020, wherein consulting physicians, pulmonologists, diabetologists, obstetricians/gynecologists, or cardiologists across 14 cities completed a 39-item questionnaire consisting of 3 sections, one each on awareness, attitude, and practice patterns. Descriptive statistics were used to summarize the study results. Statistical analysis was performed for comparison of subgroups by physician specialty, city of practice (metro/non-metro), and zone of practice (north/south/east/west). Level of statistical significance was set at p < 0.05.

Results: In all, 780 physicians completed the survey. Of these, 3.97, 53.08, and 42.95% had high, medium, and low level of awareness about influenza/influenza vaccination, respectively. Statistically significant (p < 0.05) between-group differences were found by physician specialty and zone of practice. In terms of attitude toward vaccination of high-risk group subjects, only 0.9% physicians were “extremely concerned,” while the majority (92.56%) were “quite concerned” and 6.54% were a “little concerned,” with no reported significant differences between different subgroups. With regard to practice patterns, 82.82% of physicians offered influenza vaccines to their patients, 32.69% vaccinated 10–25% of patients per month, and 38.85% required and offered the vaccine to their office staff. Physicians' reasons for not prescribing influenza vaccines to patients included fear of side effects (16.54%), cost (15.64%), lack of awareness about availability (15.38%), absence of belief that it is beneficial (14.36%), history of side effects (13.46%), and patients' fear of needles (11.28%).

Conclusion: These findings suggest the need to implement educational strategies among physicians to enhance their awareness about influenza vaccination and improve their attitudes and current practices toward influenza vaccination especially in high-risk groups in India.

The Mechanism behind Influenza Virus Cytokine Storm

Influenza viruses are still a serious threat to human health. Cytokines are essential for cell-to-cell communication and viral clearance in the immune system, but excessive cytokines can cause serious immune pathology. Deaths caused by severe influenza are usually related to cytokine storms. The recent literature has described the mechanism behind the cytokine-storm network and how it can exacerbate host pathological damage. Biological factors such as sex, age, and obesity may cause biological differences between different individuals, which affects cytokine storms induced by the influenza virus. In this review, we summarize the mechanism behind influenza virus cytokine storms and the differences in cytokine storms of different ages and sexes, and in obesity.

Estimating infectiousness throughout SARS-CoV-2 infection course

Two elementary parameters for quantifying viral infection and shedding are viral load and whether samples yield a replicating virus isolate in cell culture. We examined 25,381 cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Germany, including 6110 from test centers attended by presymptomatic, asymptomatic, and mildly symptomatic (PAMS) subjects, 9519 who were hospitalized, and 1533 B.1.1.7 lineage infections. The viral load of the youngest subjects was lower than that of the older subjects by 0.5 (or fewer) log10 units, and they displayed an estimated ~78% of the peak cell culture replication probability; in part this was due to smaller swab sizes and unlikely to be clinically relevant. Viral loads above 109 copies per swab were found in 8% of subjects, one-third of whom were PAMS, with a mean age of 37.6 years. We estimate 4.3 days from onset of shedding to peak viral load (108.1 RNA copies per swab) and peak cell culture isolation probability (0.75). B.1.1.7 subjects had mean log10 viral load 1.05 higher than that of non-B.1.1.7 subjects, and the estimated cell culture replication probability of B.1.1.7 subjects was higher by a factor of 2.6.

Incorporating Real-time Influenza Detection Into the Test-negative Design for Estimating Influenza Vaccine Effectiveness: The Real-time Test-negative Design (rtTND)

With rapid and accurate molecular influenza testing now widely available in clinical settings, influenza vaccine effectiveness (VE) studies can prospectively select participants for enrollment based on real-time results rather than enrolling all eligible patients regardless of influenza status, as in the traditional test-negative design (TND). Thus, we explore advantages and disadvantages of modifying the TND for estimating VE by using real-time, clinically available viral testing results paired with acute respiratory infection eligibility criteria for identifying influenza cases and test-negative controls prior to enrollment. This modification, which we have called the real-time test-negative design (rtTND), has the potential to improve influenza VE studies by optimizing the case-to-test-negative control ratio, more accurately classifying influenza status, improving study efficiency, reducing study cost, and increasing study power to adequately estimate VE. Important considerations for limiting biases in the rtTND include the need for comprehensive clinical influenza testing at study sites and accurate influenza tests.

Viral Kinetics and Resistance Development in Children Treated with Neuraminidase Inhibitors: The Influenza Resistance Information Study (IRIS)

Background

We studied the effect of age, baseline viral load, vaccination status, antiviral therapy, and emergence of drug resistance on viral shedding in children infected with influenza A or B virus.

Methods

Samples from children (aged ≤13 years) enrolled during the 7 years of the prospective Influenza Resistance Information Study were analyzed using polymerase chain reaction to determine the influenza virus (sub-)type, viral load, and resistance mutations. Disease severity was assessed; clinical symptoms were recorded. The association of age with viral load and viral clearance was examined by determining the area under the curve for viral RNA shedding using logistic regression and Kaplan-Meier analyses.

Results

A total of 2131 children infected with influenza (683, A/H1N1pdm09; 825, A/H3N2; 623, influenza B) were investigated. Age did not affect the mean baseline viral load. Children aged 1−5 years had prolonged viral RNA shedding (±1–2 days) compared with older children and up to 1.2-fold higher total viral burden. Besides, in older age (odds ratio [OR], 1.08; confidence interval [CI], 1.05–1.12), prior vaccination status (OR, 1.72; CI, 1.22–2.43) and antiviral treatment (OR, 1.74; CI, 1.43–2.12) increased the rate of viral clearance. Resistance mutations were detected in 49 children infected with influenza A virus (34, A/H1N1pdm09; 15, A/H3N2) treated with oseltamivir, most of whom were aged <5 years (n = 39).

Conclusions

Children aged 1−5 years had a higher total viral burden with prolonged virus shedding and had an increased risk of acquiring resistance mutations following antiviral treatment.

Clinical Trials Registration

NCT00884117.

Heterogeneity in transmissibility and shedding SARS-CoV-2 via droplets and aerosols

Background

Which virological factors mediate overdispersion in the transmissibility of emerging viruses remains a long-standing question in infectious disease epidemiology.

Methods

Here, we use systematic review to develop a comprehensive dataset of respiratory viral loads (rVLs) of SARS-CoV-2, SARS-CoV-1 and influenza A(H1N1)pdm09. We then comparatively meta-analyze the data and model individual infectiousness by shedding viable virus via respiratory droplets and aerosols.

Results

The analyses indicate heterogeneity in rVL as an intrinsic virological factor facilitating greater overdispersion for SARS-CoV-2 in the COVID-19 pandemic than A(H1N1)pdm09 in the 2009 influenza pandemic. For COVID-19, case heterogeneity remains broad throughout the infectious period, including for pediatric and asymptomatic infections. Hence, many COVID-19 cases inherently present minimal transmission risk, whereas highly infectious individuals shed tens to thousands of SARS-CoV-2 virions/min via droplets and aerosols while breathing, talking and singing. Coughing increases the contagiousness, especially in close contact, of symptomatic cases relative to asymptomatic ones. Infectiousness tends to be elevated between 1 and 5 days post-symptom onset.

Conclusions

Intrinsic case variation in rVL facilitates overdispersion in the transmissibility of emerging respiratory viruses. Our findings present considerations for disease control in the COVID-19 pandemic as well as future outbreaks of novel viruses.

Funding

Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant program, NSERC Senior Industrial Research Chair program and the Toronto COVID-19 Action Fund.

Optimizing antiviral treatment for seasonal influenza in the USA: a mathematical modeling analysis

BACKGROUND

Seasonal influenza remains a major cause of morbidity and mortality in the USA. Despite the US Centers for Disease Control and Prevention recommendation promoting the early antiviral treatment of high-risk patients, treatment coverage remains low.

METHODS

To evaluate the population-level impact of increasing antiviral treatment timeliness and coverage among high-risk patients in the USA, we developed an influenza transmission model that incorporates data on infectious viral load, social contact, and healthcare-seeking behavior. We modeled the reduction in transmissibility in treated individuals based on their reduced daily viral load. The reduction in hospitalizations following treatment was based on estimates from clinical trials. We calibrated the model to weekly influenza data from Texas, California, Connecticut, and Virginia between 2014 and 2019. We considered in the baseline scenario that 2.7-4.8% are treated within 48 h of symptom onset while an additional 7.3-12.8% are treated after 48 h of symptom onset. We evaluated the impact of improving the timeliness and uptake of antiviral treatment on influenza cases and hospitalizations.

RESULTS

Model projections suggest that treating high-risk individuals as early as 48 h after symptom onset while maintaining the current treatment coverage level would avert 2.9-4.5% of all symptomatic cases and 5.5-7.1% of all hospitalizations. Geographic variability in the effectiveness of earlier treatment arises primarily from variabilities in vaccination coverage and population demographics. Regardless of these variabilities, we found that when 20% of the high-risk individuals were treated within 48 h, the reduction in hospitalizations doubled. We found that treatment of the elderly population (> 65 years old) had the highest impact on reducing hospitalizations, whereas treating high-risk individuals aged 5-19 years old had the highest impact on reducing transmission. Furthermore, the population-level benefit per treated individual is enhanced under conditions of high vaccination coverage and a low attack rate during an influenza season.

CONCLUSIONS

Increased timeliness and coverage of antiviral treatment among high-risk patients have the potential to substantially reduce the burden of seasonal influenza in the USA, regardless of influenza vaccination coverage and the severity of the influenza season.

Seasonal influenza during pregnancy

Seasonal Influenza is an acute respiratory illness caused by Influenza A or B viruses. Its presentation is commonly with signs and symptoms of upper respiratory tract involvement such as cough, sore throat and runny nose, associated with generalized systemic symptoms such as fever, headaches, myalgia, and weakness. The severity of symptoms is very variable, ranging from mild self-limiting infection to severe acute respiratory illness requiring intensive interventions. It usually occurs during the winter season and can lead to outbreaks and epidemics worldwide. Influenza is associated with increased morbidity and mortality in high-risk populations including pregnant women and up to two weeks postpartum. Rapid and accurate diagnosis of Influenza is necessary for prompt treatment to reduce morbidity. General public health measures and vaccination are recommended to reduce morbidity and control the spread of the disease. There are many published articles on the several Influenza epidemics that have occurred in this century. In this article, we aim to review the epidemiology, clinical manifestations, diagnosis, treatment, and prevention of seasonal Influenza during pregnancy. We performed an electronic search on PubMed, Cochrane database, National guidelines clearing house and Google Scholar databases.

Comparison of Clinical and Epidemiological Characteristics of Asymptomatic and Symptomatic SARS-CoV-2 Infection in Children

To understand the epidemiological and clinical features of the symptomatic and asymptomatic pediatric cases of COVID-19, we carried out a prospective study in Shanghai during the period of January 19 to April 30, 2020. A total of 49 children (mean age 11.5 ± 5.12 years) confirmed with SARS-CoV-2 infection were enrolled in the study, including 11 (22.4%) domestic cases and 38 (77.6%) imported cases. Nine (81.8%) local cases and 12 (31.6%) imported cases had a definitive epidemiological exposure. Twenty-eight (57.1%) were symptomatic and 21 (42.9%) were asymptomatic. Neither asymptomatic nor symptomatic cases progressed to severe diseases. The mean duration of viral shedding for SARS-CoV-2 in upper respiratory tract was 14.1 ± 6.4 days in asymptomatic cases and 14.8 ± 8.4 days in symptomatic cases (P > 0.05). Forty-five (91.8%) cases had viral RNA detected in stool. The mean duration of viral shedding in stool was 28.1 ± 13.3 days in asymptomatic cases and 30.8 ± 18.6 days in symptomatic participants (P > 0.05). Children < 7 years shed viral RNA in stool for a longer duration than school-aged children (P < 0.05). Forty-three (87.8%) cases had seropositivity for antibodies against SARS-CoV-2 within 1-3 weeks after confirmation with infection. In conclusion, asymptomatic SARS-CoV-2 infection may be common in children in the community during the COVID-19 pandemic wave. Asymptomatic cases shed viral RNA in a similar pattern as symptomatic cases do. It is of particular concern that asymptomatic individuals are potentially seed transmission of SARS-CoV-2 and pose a challenge to disease control.

The Role of Type I IFNs in Influenza: Antiviral Superheroes or Immunopathogenic Villains?

The important role of interferons (IFNs) in antiviral innate immune defense is well established. Although recombinant IFN-α was approved for cancer and chronic viral infection treatment by regulatory agencies in many countries starting in 1986, no IFNs are approved for treatment of influenza A virus (IAV) infection. This is partially due to the complex effects of IFNs in acute influenza infection. IAV attacks the human respiratory system and causes significant morbidity and mortality globally. During influenza infection, depending on the strain of IAV and the individual host, type I IFNs can have protective antiviral effects or can contribute to immunopathology. In the context of virus infection, the immune system has complicated mechanisms regulating the expression and effects of type I IFN to maximize the antiviral response by both activating and enhancing beneficial innate cell function, while limiting immunopathological responses that lead to exaggerated tissue damage. In this review, we summarize the complicated, but important, role of type I IFNs in influenza infections. This includes both protective and harmful effects of these important cytokines during infection.

Development of an RNA Strand-Specific Hybridization Assay To Differentiate Replicating versus Nonreplicating Influenza A Viruses

Replication of influenza A virus (IAV) from negative-sense viral RNA (vRNA) requires the generation of positive-sense RNA (+RNA). Most molecular assays, such as conventional real-time reverse transcriptase PCR (rRT-PCR), detect total RNA in a sample without differentiating vRNA from +RNA. These assays are not designed to distinguish IAV infection versus exposure of an individual to an environment enriched with IAVs but wherein no viral replication occurs. We therefore developed a strand-specific hybridization (SSH) assay that differentiates between vRNA and +RNA and quantifies relative levels of each RNA species. The SSH assay exhibited a linearity of 7 logs with a lower limit of detection of 6.0 × 10² copies of molecules per reaction. No signal was detected in samples with a high load of nontarget template or influenza B virus, demonstrating assay specificity. IAV +RNA was detected 2 to 4 h postinoculation of MDCK cells, whereas synthesis of cold-adapted IAV +RNA was significantly impaired at 37°C. The SSH assay was then used to test IAV rRT-PCR positive nasopharyngeal specimens collected from individuals exposed to IAV at swine exhibitions (n = 7) or while working at live bird markets (n = 2). The SSH assay was able to differentiate vRNA and +RNA in samples collected from infected, symptomatic individuals versus individuals who were exposed to IAV in the environment but had no active viral replication. Data generated with this technique, especially when coupled with clinical data and assessment of seroconversion, will facilitate differentiation of actual IAV infection with replicating virus versus individuals exposed to high levels of environmental contamination but without virus infection.

Influenza A(H1N1)pdm09 infection and viral load analysis in patients with different clinical presentations

BACKGROUND

Influenza viral load (VL) can be a decisive factor in determining the antiviral efficacy in viral clearance.

OBJECTIVE

This study aimed to evaluate the rate of infection and the role of influenza VL on the clinical spectrum of illnesses among different patient groups attended at a tertiary hospital in Brazil.

METHODS

Samples were collected from patients presenting acute respiratory infection from 2009 to 2013. Overall, 2262 samples were analysed and distributed into three groups: (i) asymptomatic (AS); (ii) symptomatic outpatients (OP); and (iii) hospitalised patients (HP). VL (expressed in Log10 RNA copies/mL) was calculated through a quantitative real-time one-step reverse transcription-polymerase chain reaction (RT-PCR) assay aimed at the M gene, with human RNAseP target as internal control and normalising gene of threshold cycle values.

FINDINGS

A total of 162 (7.16%) H1N1pdm09 positive samples were analysed. Patients aged from 0.08 to 77 years old [median ± standard deviation (SD): 12.5 ± 20.54]. Children with 5 to 11 years old presented the highest detection (p < 0.0001). AS patients had the lowest VL, with a significant difference when compared with symptomatic patients (p = 0.0003). A higher VL was observed within two days of disease onset. Ten patients (HP group) received antiviral treatment and were followed up and presented a mean initial VL of 6.64 ± 1.82. A complete viral clearance for 50% of these patients was reached after 12 days of treatment.

MAIN CONCLUSIONS

It is important to evaluate AS patients as potential spreaders, as viral shedding was still present, even at lower VL. Our results suggest that patients with underlying diseases and severe clinical symptoms may be considered for prolonged viral treatment.

Are healthcare personnel at higher risk of seasonal influenza than other working adults?

Background: Adults are at risk of being exposed to influenza from many sources. Healthcare personnel (HCP) have the additional risk of being exposed to ill patients.

Objective:

To determine whether HCP were at higher risk than adults working in nonhealthcare roles (non-HCP).

Design:

Prospective cohort study.

Setting:

Acute-care hospitals and other businesses in Toronto, Ontario, Canada.

Methods:

Adults aged 18–69 years were enrolled for 1 or more of the 2010/2011, 2011/2012, and 2012/2013 influenza seasons. Swabs collected during acute respiratory illnesses were tested for influenza and pre- and postseason blood samples were tested for influenza-specific immune response.

Results:

The adjusted odds of influenza were similar for HCP and non-HCP (odds ratio [OR], 1.29; 95% confidence interval [CI], 0.63–2.63). Older adults and those vaccinated against influenza had lower odds, and those who shared their workspace and who used corrective eyewear had higher odds of influenza.

Conclusions:

HCP and other working adults are at similar risk of influenza infection.

Estimating Transmission Potential of H5N1 Viruses Among Humans in Egypt Using Phylogeny, Genetic Distance and Sampling Time Interval

In 2014 and 2015, the number of human cases of H5N1 avian influenza virus infections had increased dramatically in Egypt. This increase might be related to increase in the transmission potential of the virus among humans. To clarify the cause of the increase in H5N1 human cases, we investigate the transmissibility of H5N1 viruses among humans via estimating the basic reproduction number R₀ using nucleotide sequences and sampling dates of viruses. To this end, full-length hemagglutinin gene sequences of human and avian H5N1 influenza viruses isolated from 2006 to 2016 in Egypt were obtained from the NCBI influenza virus resource. Taking into account the phylogeny, genetic distance, sampling time difference among viruses, R₀ was estimated to be 0.05 (95% CI: 0.01, 0.13) assuming that human-to-human transmissions occurred within a city, 0.23(95% CI: 0.14, 0.35) assuming human-to-human transmissions among cities. Our results indicate that human-to-human transmission of H5N1 viruses in Egypt is limited, and the large increase in human cases is likely attributed to other factor than increase in human-to-human transmission potential.

Airborne Transmission of Influenza Virus in a Hospital of Qinhuangdao During 2017-2018 Flu Season

The 2017-2018 flu season is considered to be one of the most severe, with numerous influenza outbreaks worldwide. In an infectious disease hospital of Qinhuangdao, air samples were collected daily from outpatient hall, clinical laboratory, fever clinic, children's ward (Children's Ward I/Children's Ward II), and adult ward during 23-29 January 2018 (peak flu activity) and 9-15 April 2018 (low flu activity). The air samples were collected with SLC-SiOH magnetic beads using impingement samplers. Real-time PCR assay was used to detect the RNA of airborne influenza (IFVA and IFVB) in the 91 collected aerosol samples. The results indicated that the air samples collected from the children's wards, adult ward and fever clinic were detected with airborne influenza viruses. However, the samples collected from outpatient hall and clinical laboratory were absence of influenza viruses. In addition, the subtypes of pH1N1/IFVA, H3N2/IFVA, yamagata/IFVB, and victoria/IFVB were detected among the samples with positive IFVA and IFVB. Notably, a new developed subtype of pH1N1 (an epidemic in 2018) was detected in the aerosol samples. In summary, this study profiled the distribution of airborne influenza in an infectious hospital in Qinhuangdao during 2017-2018 flu season. Patients infected with influenza could release airborne particles containing the virus into their environment. Healthcare workers and visitors in those places might have frequent exposure to airborne influenza virus. Therefore, we recommend some protective measures such as air disinfection and mask wearing to prevent and control the transmission of airborne influenza in hospital.

The respiratory microbiota: associations with influenza symptomatology and viral shedding

PURPOSE

Manifestations of infection and the degree of influenza virus vary. We hypothesized that the nose/throat microbiota modifies the duration of influenza symptoms and viral shedding. Exploring these relationships may help identify additional methods for reducing influenza severity and transmission.

METHODS

Using a household transmission study in Nicaragua, we identified secondary cases of influenza virus infection, defined as contacts with detectable virus or a greater than 4-fold change in hemagglutinin inhibition antibody titer. We characterized the nose/throat microbiota of secondary cases before infection and explored whether the duration of symptoms and shedding differed by bacterial community characteristics.

RESULTS

Among 124 secondary cases of influenza, higher bacterial community diversity before infection was associated with longer shedding duration (Shannon acceleration factor [AF]: 1.61, 95% confidence interval [CI]: 1.24, 2.10) and earlier time to infection (Shannon AF: 0.72, 95% CI: 0.53, 0.97; Chao1 AF: 0.992, 95% CI: 0.986, 0.998). Neisseria and multiple other oligotypes were significantly associated with symptom and shedding durations and time to infection.

CONCLUSIONS

The nose/throat microbiota before influenza virus infection was associated with influenza symptoms and shedding durations. Further studies are needed to determine if the nose/throat microbiota is a viable target for reducing influenza symptoms and transmission.

Cellular DNA quantification in respiratory samples for the normalization of viral load: a real need?

•

Higher number of cells was observed in virus-pos as compared to virus-neg samples.

•

No difference in the kinetics of viral shedding was observed.

•

The flocked swab is a valid alternative to commonly used specimen collection tools.

•

Normalization seems to be unnecessary in samples collected with flocked nasal swabs.

Background

Respiratory tract infections have an enormous social economic impact, with high incidence of hospitalization and high costs. Adequate specimen collection is the first crucial step for the correct diagnosis of viral respiratory infections.

Objectives

The present retrospective study aimed: i) to verify the cell yield obtained from sampling the nasal respiratory tract using mid-turbinate flocked swabs; ii) to evaluate the normalization of viral load, based on cell number; and iii) to compare the kinetics of viral infection obtained with normalized vs non-normalized viral load.

Study design

The number of cells were quantified by real-time PCR in residual extract of nasal swabs tested for respiratory viruses detection and stored at −80 °C in a universal transport medium (UTM™).

Results

A total of 513 virus-positive and 226 virus-negative samples were analyzed. Overall, a median of 4.42 log₁₀ β2-microgolubin DNA copy number/ml of UTM^™ (range 1.17–7.26) was detected. A significantly higher number of cells was observed in virus-positive as compared to virus-negative samples (4.75 vs 3.76; p < 0.001). Viral loads expressed as log₁₀ RNA copies/ml of UTM^™ and log₁₀ RNA copies/median number of cells were compared in virus-positive samples and a strict correlation (r = 0.89, p < 0.001) and agreement (R2 = 0.82) were observed. In addition, infection kinetics were compared using the two methods with a follow-up series of eight episodes of viral infection and the mean difference was -0.57 log₁₀ (range −1.99 to 0.40).

Conclusions

The normalization of viral load using cellular load compliments the validation of real-time PCR results in the diagnosis of respiratory viruses but is not strictly needed.

Pathogen Clearance and New Respiratory Tract Infections Among Febrile Children in Zanzibar Investigated With Multitargeting Real-Time Polymerase Chain Reaction on Paired Nasopharyngeal Swab Samples

BACKGROUND

New molecular methods have revealed frequent and often polymicrobial respiratory infections in children in low-income settings. It is not known whether presence of multiple pathogens is due to prolonged infections or to frequent exposure. The aim of this study was to analyze short-term pathogen clearance from nasopharynx and the rate of new respiratory tract infections in febrile preschool children.

METHODS

Children (n = 207) with uncomplicated acute febrile illness 2-59 months of age presenting to a health center in Zanzibar, Tanzania, April-July 2011, were included. Paired nasopharyngeal swab samples, collected at enrolment and after 14 days, were analyzed by multiple real-time polymerase chain reaction for Adenovirus, bocavirus, Bordetella pertussis, Chlamydophila pneumoniae, Coronaviruses, Enterovirus, influenza A and B virus, metapneumovirus, measles virus, Mycoplasma pneumoniae, parainfluenza virus, Parechovirus, respiratory syncytial virus and Rhinovirus. An age-matched and geographically matched healthy control group (n = 166) underwent nasopharyngeal sampling on 1 occasion.

RESULTS

At baseline, 157/207 (76%) patients had at least 1 pathogen detected, in total 199 infections. At follow-up (day 14), 162/199 (81%) of these infections were not detected, including >95% of the previously detected infections with Enterovirus, influenza A virus, influenza B virus, metapneumovirus or parainfluenza virus. Still 115 (56%) children were positive for at least 1 pathogen at follow-up, of which 95/115 (83%) were not found at baseline. Detection of influenza B on day 14 was significantly associated with fever during follow-up.

CONCLUSION

The results suggest that children with acute febrile illness in Zanzibar rapidly clear respiratory tract infections but frequently acquire new infections within 14 days.

Inflammatory Monocytes Drive Influenza A Virus-Mediated Lung Injury in Juvenile Mice

Healthy children are more likely to die of influenza A virus (IAV) infection than healthy adults. However, little is known about the mechanisms underlying the impact of young age on the development of life-threatening IAV infection. We report increased mortality in juvenile mice compared with adult mice at each infectious dose of IAV. Juvenile mice had sustained elevation of type I IFNs and persistent NLRP3 inflammasome activation in the lungs, both of which were independent of viral titer. Juvenile mice, but not adult mice, had increased MCP-1 levels that remained high even after viral clearance. Importantly, continued production of MCP-1 was associated with persistent recruitment of monocytes to the lungs and prolonged elevation of inflammatory cytokines. Transcriptional signatures of recruited monocytes to the juvenile and adult IAV-infected lungs were assessed by RNA-seq. Genes associated with a proinflammatory signature were upregulated in the juvenile monocytes compared with adult monocytes. Depletion of monocytes with anti-CCR2 Ab decreased type I IFN secretion, NLRP3 inflammasome activation, and lung injury in juvenile mice. This suggests an exaggerated inflammatory response mediated by increased recruitment of monocytes to the lung, and not an inability to control viral replication, is responsible for severe IAV infection in juvenile mice. This study provides insight into severe IAV infection in juveniles and identifies key inflammatory monocytes that may be central to pediatric acute lung injury secondary to IAV.

Viral Shedding and Transmission Potential of Asymptomatic and Paucisymptomatic Influenza Virus Infections in the Community

Background

Influenza virus infections are associated with a wide spectrum of disease. However, few studies have investigated in detail the epidemiological and virological characteristics of asymptomatic and mild illness with influenza virus infections.

Methods

In a community-based study in Hong Kong from 2008 to 2014, we followed up initially healthy individuals who were household contacts of symptomatic persons with laboratory-confirmed influenza, to identify secondary infections. Information from daily symptom diaries was used to classify infections as symptomatic (≥2 signs/symptoms, including fever ≥37.8°C, headache, myalgia, cough, sore throat, runny nose and sputum), paucisymptomatic (1 symptom only), or asymptomatic (none of these symptoms). We compared the patterns of influenza viral shedding between these groups.

Results

We identified 235 virologically confirmed secondary cases of influenza virus infection in the household setting, including 31 (13%) paucisymptomatic and 25 (11%) asymptomatic cases. The duration of viral RNA shedding was shorter and declined more rapidly in paucisymptomatic and asymptomatic than in symptomatic cases. The mean levels of influenza viral RNA shedding in asymptomatic and paucisymptomatic cases were approximately 1-2 log10 copies lower than in symptomatic cases.

Conclusions

The presence of influenza viral shedding in patients with influenza who have very few or no symptoms reflects their potential for transmitting the virus to close contacts. These findings suggest that further research is needed to investigate the contribution of persons with asymptomatic or clinically mild influenza virus infections to influenza virus transmission in household, institutional, and community settings.

Influenza in long-term care facilities

Long-term care facility environments and the vulnerability of their residents provide a setting conducive to the rapid spread of influenza virus and other respiratory pathogens. Infections may be introduced by staff, visitors or new or transferred residents, and outbreaks of influenza in such settings can have devastating consequences for individuals, as well as placing extra strain on health services. As the population ages over the coming decades, increased provision of such facilities seems likely. The need for robust infection prevention and control practices will therefore remain of paramount importance if the impact of outbreaks is to be minimised. In this review, we discuss the nature of the problem of influenza in long-term care facilities, and approaches to preventive and control measures, including vaccination of residents and staff, and the use of antiviral drugs for treatment and prophylaxis, based on currently available evidence.

Predictors of influenza a molecular viral shedding in Hutterite communities

BACKGROUND

Patterns of influenza molecular viral shedding following influenza infection have been well established; predictors of viral shedding however remain uncertain.

OBJECTIVES

We sought to determine factors associated with peak molecular viral load, duration of shedding, and viral area under the curve (AUC) in children and adult Hutterite colony members with laboratory-confirmed influenza.

METHODS

A cohort study was conducted in Hutterite colonies in Alberta, Canada. Flocked nasal swabs were collected during three influenza seasons (2007-2008 to 2009-2010) from both symptomatic and asymptomatic individuals infected with influenza. Samples were tested by real-time reverse-transcription polymerase chain reaction for influenza A and influenza B, and the viral load was determined for influenza A-positive samples.

RESULTS

For seasonal H1N1, younger age was associated with a larger AUC, female sex was associated with decreased peak viral load and reduced viral shedding duration, while the presence of comorbidity was associated with increased peak viral load. For H3N2, younger age was associated with increased peak viral load and increased AUC. For pandemic H1N1, younger age was associated with increased peak viral load and increased viral AUC, female sex was associated with reduced peak viral load, while inapparent infection was associated with reduced peak viral load, reduced viral shedding duration, and reduced viral AUC.

CONCLUSIONS

Patterns of molecular viral shedding vary by age, sex, comorbidity, and the presence of symptoms. Predictor variables vary by influenza A subtype.

Quantifying the contribution of asymptomatic infection to the cumulative incidence

Many infectious diseases in humans may manifest with no or mild symptoms. While numerous studies have estimated the proportion of infectious individuals in whom symptoms are absent during the entire course of infection, the contribution of asymptomatic cases to the overall cumulative incidence is difficult to untangle. Here, with a mathematical model, we provide a simple analytical formula to quantify this contribution and highlight the potential for large errors that can arise when naively estimating it.

Immune history and influenza virus susceptibility

Antibody responses to influenza viruses are critical for protection, but the ways in which repeated viral exposures shape antibody evolution and effectiveness over time remain controversial. Early observations demonstrated that viral exposure history has a profound effect on the specificity and magnitude of antibody responses to a new viral strain, a phenomenon called 'original antigenic sin.' Although 'sin' might suppress some aspects of the immune response, so far there is little indication that hosts with pre-existing immunity are more susceptible to viral infections compared to naïve hosts. However, the tendency of the immune response to focus on previously recognized conserved epitopes when encountering new viral strains can create an opportunity cost when mutations arise in these conserved epitopes. Hosts with different exposure histories may continue to experience distinct patterns of infection over time, which may influence influenza viruses' continued antigenic evolution. Understanding the dynamics of B cell competition that underlie the development of antibody responses might help explain the low effectiveness of current influenza vaccines and lead to better vaccination strategies.

Estimation of influenza-attributable medically attended acute respiratory illness by influenza type/subtype and age, Germany, 2001/02-2014/15

Background

The total burden of influenza in primary care is difficult to assess. The case definition of medically attended “acute respiratory infection” (MAARI) in the German physician sentinel is sensitive; however, it requires modelling techniques to derive estimates of disease attributable to influenza. We aimed to examine the impact of type/subtype and age.

Methods

Data on MAARI and virological results of respiratory samples (virological sentinel) were available from 2001/02 until 2014/15. We constructed a generalized additive regression model for the periodic baseline and the secular trend. The weekly number of influenza‐positive samples represented influenza activity. In a second step, we distributed the estimated influenza‐attributable MAARI (iMAARI) according to the distribution of types/subtypes in the virological sentinel.

Results

Season‐specific iMAARI ranged from 0.7% to 8.9% of the population. Seasons with the strongest impact were dominated by A(H3), and iMAARI attack rate of the pandemic 2009 (A(H1)pdm09) was 4.9%. Regularly the two child age groups (0‐4 and 5‐14 years old) had the highest iMAARI attack rates reaching frequently levels up to 15%‐20%. Influenza B affected the age group of 5‐ to 14‐year‐old children substantially more than any other age group. Sensitivity analyses demonstrated both comparability and stability of the model.

Conclusion

We constructed a model that is well suited to estimate the substantial impact of influenza on the primary care sector. A(H3) causes overall the greatest number of iMAARI, and influenza B has the greatest impact on school‐age children. The model may incorporate time series of other pathogens as they become available.

Maternal vitamin D supplementation during pregnancy and lactation to prevent acute respiratory infections in infancy in Dhaka, Bangladesh (MDARI trial): protocol for a prospective cohort study nested within a randomized controlled trial

Background

Early infancy is a high-risk period for severe acute respiratory infection (ARI), particularly in low-income countries with resource-limited health systems. Lower respiratory tract infection (LRTI) is commonly preceded by upper respiratory infection (URTI), and often caused by respiratory syncytial virus (RSV), influenza and other common community-acquired viral pathogens. Vitamin D status is a candidate modifiable early-life determinant of the host antiviral immune response and thus may influence the risk of ARI-associated morbidity in high-risk populations.

Methods/Design

In the Maternal Vitamin D for Infant Growth (MDIG) study in Dhaka, Bangladesh (NCT01924013), 1300 pregnant women are randomized to one of five groups: placebo, 4200 IU/week, 16,800 IU/week, or 28,000 IU/week from 2^nd trimester to delivery plus placebo from 0–6 months postpartum; or, 28,000 IU/week prenatal and until 6-months postpartum. In the Maternal Vitamin D for ARI in Infancy (MDARI) sub-study nested within the MDIG trial, trained personnel conduct weekly postnatal home visits to inquire about ARI symptoms and conduct a standardized clinical assessment. Supplementary home visits between surveillance visits are conducted when caregivers make phone notifications of new infant symptoms. Mid-turbinate nasal swab samples are obtained from infants who meet standardized clinical ARI criteria. Specimens are tested by polymerase chain reaction (PCR) for 8 viruses (influenza A/B, parainfluenza 1/2/3, RSV, adenovirus, and human metapneumovirus), and nasal carriage density of Streptococcus pneumoniae. The primary outcome is the incidence rate of microbiologically-positive viral ARI, using incidence rate ratios to estimate between-group differences. We hypothesize that among infants 0–6 months of age, the incidence of microbiologically-confirmed viral ARI will be significantly lower in infants whose mothers received high-dose prenatal/postpartum vitamin D supplements versus placebo. Secondary outcomes include incidence of ARI associated with specific pathogens (influenza A or B, RSV), clinical ARI, and density of pneumococcal carriage.

Discussion

If shown to reduce the risk of viral ARI in infancy, integration of maternal prenatal/postpartum vitamin D supplementation into antenatal care programs in South Asia may be a feasible primary preventive strategy to reduce the burden of ARI-associated morbidity and mortality in young infants.

Trial registration

NCT02388516, registered March 9, 2015.

Vaccination of healthcare workers: A review

Vaccine-preventable diseases are a significant cause of morbidity and mortality. As new vaccines are proving to be effective and as the incidence of some infections decreases, vaccination practices are changing. Healthcare workers (HCWs) are particularly exposed to and play a role in nosocomial transmission, which makes them an important target group for vaccination. Most vaccine-preventable diseases still carry a significant risk of resurgence and have caused outbreaks in recent years. While many professional societies favor vaccination of HCWs as well as the general population, recommendations differ from country to country. In turn, vaccination coverage varies widely for each microorganism and for each country, making hospitals and clinics vulnerable to outbreaks. Vaccine mandates and non-mandatory strategies are the subject of ongoing research and controversies. Optimal approaches to increase coverage and turn the healthcare workforce into an efficient barrier against infectious diseases are still being debated.

Review Article: The Fraction of Influenza Virus Infections That Are Asymptomatic: A Systematic Review and Meta-analysis

BACKGROUND

The fraction of persons with influenza virus infection, who do not report any signs or symptoms throughout the course of infection is referred to as the asymptomatic fraction.

METHODS

We conducted a systematic review and meta-analysis of published estimates of the asymptomatic fraction of influenza virus infections. We found that estimates of the asymptomatic fraction were reported from two different types of studies: first, outbreak investigations with short-term follow-up of potentially exposed persons and virologic confirmation of infections; second, studies conducted across epidemics typically evaluating rates of acute respiratory illness among persons with serologic evidence of infection, in some cases adjusting for background rates of illness from other causes.

RESULTS

Most point estimates from studies of outbreak investigations fell in the range 4%-28% with low heterogeneity (I = 0%) with a pooled mean of 16% (95% confidence interval = 13%, 19%). Estimates from the studies conducted across epidemics without adjustment were very heterogeneous (point estimates 0%-100%; I = 97%), while estimates from studies that adjusted for background illnesses were more consistent with point estimates in the range 65%-85% and moderate heterogeneity (I = 58%). Variation in estimates could be partially explained by differences in study design and analysis, and inclusion of mild symptomatic illnesses as asymptomatic in some studies.

CONCLUSIONS

Estimates of the asymptomatic fraction are affected by the study design, and the definitions of infection and symptomatic illness. Considerable differences between the asymptomatic fraction of infections confirmed by virologic versus serologic testing may indicate fundamental differences in the interpretation of these two indicators.

Individual Correlates of Infectivity of Influenza A Virus Infections in Households

BACKGROUND

Identifying individual correlates of infectivity of influenza virus is important for disease control and prevention. Viral shedding is used as a proxy measure of infectivity in many studies. However, the evidence for this is limited.

METHODS

In a detailed study of influenza virus transmission within households in 2008-12, we recruited index cases with confirmed influenza infection from outpatient clinics, and followed up their household contacts for 7-10 days to identify secondary infections. We used individual-based hazard models to characterize the relationship between individual viral shedding and individual infectivity.

RESULTS

We analyzed 386 households with 1147 household contacts. Index cases were separated into 3 groups according to their estimated level of viral shedding at symptom onset. We did not find a statistically significant association of virus shedding with transmission. Index cases in medium and higher viral shedding groups were estimated to have 21% (95% CI: -29%, 113%) and 44% (CI: -16%, 167%) higher infectivity, compared with those in the lower viral shedding group.

CONCLUSIONS

Individual viral load measured by RT-PCR in the nose and throat was at most weakly correlated with individual infectivity in households. Other correlates of infectivity should be examined in future studies.

The Timeline of Influenza Virus Shedding in Children and Adults in a Household Transmission Study of Influenza in Managua, Nicaragua

In a household transmission study in Nicaragua, children under 6 years old had a longer duration of presymptomatic influenza virus shedding than adults. The duration of postsymptomatic influenza virus shedding was longest in children 0-5 years old, followed by children 6-15 years of age and adults.

Viable influenza A virus in airborne particles expelled during coughs versus exhalations

Background

To prepare for a possible influenza pandemic, a better understanding of the potential for the airborne transmission of influenza from person to person is needed.

Objectives

The objective of this study was to directly compare the generation of aerosol particles containing viable influenza virus during coughs and exhalations.

Methods

Sixty‐one adult volunteer outpatients with influenza‐like symptoms were asked to cough and exhale three times into a spirometer. Aerosol particles produced during coughing and exhalation were collected into liquid media using aerosol samplers. The samples were tested for the presence of viable influenza virus using a viral replication assay (VRA).

Results

Fifty‐three test subjects tested positive for influenza A virus. Of these, 28 (53%) produced aerosol particles containing viable influenza A virus during coughing, and 22 (42%) produced aerosols with viable virus during exhalation. Thirteen subjects had both cough aerosol and exhalation aerosol samples that contained viable virus, 15 had positive cough aerosol samples but negative exhalation samples, and 9 had positive exhalation samples but negative cough samples.

Conclusions

Viable influenza A virus was detected more often in cough aerosol particles than in exhalation aerosol particles, but the difference was not large. Because individuals breathe much more often than they cough, these results suggest that breathing may generate more airborne infectious material than coughing over time. However, both respiratory activities could be important in airborne influenza transmission. Our results are also consistent with the theory that much of the aerosol containing viable influenza originates deep in the lungs.

Occupational exposures to influenza among healthcare workers in the United States

The objective of this study is to estimate the annual number of occupational exposures to influenza among healthcare workers that result from providing direct and supportive care to influenza patients in acute care, home care and long-term care settings. Literature review was used to identify healthcare utilization for influenza, and worker activity patterns. This information was used, with Monte Carlo simulation, to tabulate the mean annual number of occupational exposures. Given a medium-sized epidemic with a 6% annual symptomatic influenza incidence proportion, the mean number of occupational exposures was estimated to be 81.8 million annually. Among the approximately 14 million healthcare workers, this corresponds to 5.8 exposures per worker annually, on average. Exposures, however, are likely concentrated among subsets of healthcare workers. Occupational exposures were most numerous in ambulatory care settings (38%), followed by long-term care facilities (30%) and home care settings (21%). The annual number of occupational exposures to influenza is high, but not every occupational exposure will result in infection. Some infection control activities, like patient isolation, can reduce the number of occupational exposures.

Transmission of the First Influenza A(H1N1)pdm09 Pandemic Wave in Australia Was Driven by Undetected Infections: Pandemic Response Implications

Background

During the first wave of influenza A(H1N1)pdm09 in Victoria, Australia the rapid increase in notified cases and the high proportion with relatively mild symptoms suggested that community transmission was established before cases were identified. This lead to the hypothesis that those with low-level infections were the main drivers of the pandemic.

Methods

A deterministic susceptible-infected-recovered model was constructed to describe the first pandemic wave in a population structured by disease severity levels of asymptomatic, low-level symptoms, moderate symptoms and severe symptoms requiring hospitalisation. The model incorporated mixing, infectivity and duration of infectiousness parameters to calculate subgroup-specific reproduction numbers for each severity level.

Results

With stratum-specific effective reproduction numbers of 1.82 and 1.32 respectively, those with low-level symptoms, and those with asymptomatic infections were responsible for most of the transmission. The effective reproduction numbers for infections resulting in moderate symptoms and hospitalisation were less than one. Sensitivity analyses confirmed the importance of parameters relating to asymptomatic individuals and those with low-level symptoms.

Conclusions

Transmission of influenza A(H1N1)pdm09 was largely driven by those invisible to the health system. This has implications for control measures–such as distribution of antivirals to cases and contacts and quarantine/isolation–that rely on detection of infected cases. Pandemic plans need to incorporate milder scenarios, with a graded approach to implementation of control measures.

Comparison of respiratory virus shedding by conventional and molecular testing methods in patients with haematological malignancy

Respiratory viruses (RV) are a leading cause of infection-related morbidity and mortality for patients undergoing treatment for cancer. This analysis compared duration of RV shedding as detected by culture and PCR among patients in a high-risk oncology setting (adult patients with haematological malignancy and/or stem cell transplant and all paediatric oncology patients) and determined risk factors for extended shedding. RV infections due to influenza virus, parainfluenza virus (PIV), human metapneumovirus (HMPV) and respiratory syncytial virus (RSV) from two study periods—January 2009–September 2011 (culture-based testing) and September 2011–April 2013 (PCR-based testing)—were reviewed retrospectively. Data were collected from patients in whom re-testing for viral clearance was carried out within 5–30 days after the most recent test. During the study period 456 patients were diagnosed with RV infection, 265 by PCR and 191 by culture. The median range for duration of shedding (days) by culture and PCR, respectively, were as follows—influenza virus: 13 days (5–38 days) versus 14 days (5–58 days), p 0.5; RSV: 11 days (5–35 days) versus 16 days (5–50 days), p 0.001; PIV: 9 days (5–41 days) versus 17 days (5–45 days), p ≤0.0001; HMPV 10.5 days (5–29 days) versus 14 days (5–42 days), p 0.2. In multivariable analysis, age and underlying disease or transplant were not independently associated with extended shedding regardless of testing method. In high-risk oncology settings for respiratory illness due to RSV and PIV, the virus is detectable by PCR for a longer period of time than by culture and extended shedding is observed.

The Dynamic Relationship Between Clinical Symptomatology and Viral Shedding in Naturally Acquired Seasonal and Pandemic Influenza Virus Infections

BACKGROUND

Although the pattern of viral shedding over time has been documented in volunteer challenge studies, understanding of the relationship between clinical symptomatology and viral shedding in naturally acquired influenza infections in humans remains limited.

METHODS

In a community-based study in Hong Kong from 2008 to 2014, we followed up initially healthy individuals and identified 224 secondary cases of natural influenza virus infection in the household setting. We examined the dynamic relationship between patterns of clinical symptomatology and viral shedding as quantified using reverse transcription polymerase chain reaction and viral culture in 127 cases with a clinical picture of acute respiratory infection.

RESULTS

Viral shedding in influenza A virus infections peaked on the first 1-2 days of clinical illness, and decreased gradually to undetectable levels by day 6-7, matching closely with the dynamics of clinical illness. Viral shedding in influenza B virus infections rose up to 2 days prior to symptom onset and persisted for 6-7 days after onset with a bimodal pattern.

CONCLUSIONS

Our results suggest that while clinical illness profiles may serve as a proxy for clinical infectiousness in influenza A virus infections, patients may potentially be infectious even before symptom onset or after clinical improvement in influenza B virus infections.

Natural T Cell-mediated Protection against Seasonal and Pandemic Influenza. Results of the Flu Watch Cohort Study

RATIONALE

A high proportion of influenza infections are asymptomatic. Animal and human challenge studies and observational studies suggest T cells protect against disease among those infected, but the impact of T-cell immunity at the population level is unknown.

OBJECTIVES

To investigate whether naturally preexisting T-cell responses targeting highly conserved internal influenza proteins could provide cross-protective immunity against pandemic and seasonal influenza.

METHODS

We quantified influenza A(H3N2) virus-specific T cells in a population cohort during seasonal and pandemic periods between 2006 and 2010. Follow-up included paired serology, symptom reporting, and polymerase chain reaction (PCR) investigation of symptomatic cases.

MEASUREMENTS AND MAIN RESULTS

A total of 1,414 unvaccinated individuals had baseline T-cell measurements (1,703 participant observation sets). T-cell responses to A(H3N2) virus nucleoprotein (NP) dominated and strongly cross-reacted with A(H1N1)pdm09 NP (P < 0.001) in participants lacking antibody to A(H1N1)pdm09. Comparison of paired preseason and post-season sera (1,431 sets) showed 205 (14%) had evidence of infection based on fourfold influenza antibody titer rises. The presence of NP-specific T cells before exposure to virus correlated with less symptomatic, PCR-positive influenza A (overall adjusted odds ratio, 0.27; 95% confidence interval, 0.11-0.68; P = 0.005, during pandemic [P = 0.047] and seasonal [P = 0.049] periods). Protection was independent of baseline antibodies. Influenza-specific T-cell responses were detected in 43%, indicating a substantial population impact.

CONCLUSIONS

Naturally occurring cross-protective T-cell immunity protects against symptomatic PCR-confirmed disease in those with evidence of infection and helps to explain why many infections do not cause symptoms. Vaccines stimulating T cells may provide important cross-protective immunity.

Community Surveillance of Respiratory Viruses Among Families in the Utah Better Identification of Germs-Longitudinal Viral Epidemiology (BIG-LoVE) Study

Background. This study: (1) describes the viral etiology of respiratory illness by prospectively collecting weekly symptom diaries and nasal swabs from families for 1 year, (2) analyzed data by reported symptoms, virus, age, and family composition, and (3) evaluated the duration of virus detection.

Methods. Twenty-six households (108 individuals) provided concurrent symptom and nasal swab data for 4166 person-weeks. The FilmArray polymerase chain reaction (PCR) platform (BioFire Diagnostics, LLC) was used to detect 16 respiratory viruses. Viral illnesses were defined as ≥1 consecutive weeks with the same virus detected with symptoms reported in ≥1 week.

Results. Participants reported symptoms in 23% and a virus was detected in 26% of person-weeks. Children younger than 5 years reported symptoms more often and were more likely to have a virus detected than older participants (odds ratio [OR] 2.47, 95% confidence interval [CI], 2.08–2.94 and OR 3.96, 95% CI, 3.35–4.70, respectively). Compared with single person households, individuals living with children experienced 3 additional weeks of virus detection. There were 783 viral detection episodes; 440 (56%) associated with symptoms. Coronaviruses, human metapneumovirus, and influenza A detections were usually symptomatic; bocavirus and rhinovirus detections were often asymptomatic. The mean duration of PCR detection was ≤2 weeks for all viruses and detections of ≥3 weeks occurred in 16% of episodes. Younger children had longer durations of PCR detection.

Conclusions. Viral detection is often asymptomatic and occasionally prolonged, especially for bocavirus and rhinovirus. In clinical settings, the interpretation of positive PCR tests, particularly in young children and those who live with them, may be confounded.

Analysis of influenza transmission in the households of primary and junior high school students during the 2012-13 influenza season in Odate, Japan

BACKGROUND

Households are one of the major settings of influenza transmission in the community and transmission is frequently initiated by school-aged children. We surveyed households with primary school (PS) and/ or junior high school (JH) children for the 2012-13 influenza season in Odate, Japan then characterized the epidemiology of influenza household transmission as well as estimated the serial intervals.

METHODS

We delivered a self-reported questionnaire survey to households with PS and/or JH school children in Odate City, Japan. Influenza A (H3N2) virus predominantly circulated during the 2012-13 influenza season. We investigated the epidemiological characteristics of within-household transmission and calculated the serial intervals (SI). SIs were drew by a non-parametric model and compared with parametric models by the Akaike Information Criterion. The covariable contributions were investigated by the accelerated failure model.

RESULTS

Household influenza transmission was identified in 255 out of 363 household respondents. Primary school (PS) children accounted for 45.1 % of primary cases, and disease transmission was most commonly observed between PS children and parents, followed by transmission from PS children to siblings. In primary cases of PS or JH children, younger age and longer absence from school were significantly associated with household transmission events. The mean SI was estimated as 2.8 days (95 % confidence interval 2.6-3.0 days) in the lognormal model. The estimated acceleration factors revealed that while secondary school age and the absence duration > 7 days were associated with shorter and longer SIs, respectively, antiviral prescriptions for primary cases made no contribution.

CONCLUSIONS

High frequencies of household transmission from primary school with shorter SI were found. These findings contribute to the development of future mitigation strategies against influenza transmission in Japan.

The virologist and the flu

We report a case of a virologist - who is in age-appropriate medical condition with no relevant chronic diseases - who shed influenza A H3N2 virus RNA for 70 days while infectious virus could be detected by cell culture only up to 5 days after onset of symptoms despite a 5-day course of oseltamivir. The case might have implications for infection control in hospital settings and the weighting of the predictive value of PCR results.

Investigation of an Outbreak of Variant Influenza A(H3N2) Virus Infection Associated With an Agricultural Fair-Ohio, August 2012

BACKGROUND

In 2012, one third of cases in a multistate outbreak of variant influenza A(H3N2) virus ([H3N2]v) infection occurred in Ohio. We conducted an investigation of (H3N2)v cases associated with agricultural Fair A in Ohio.

METHODS

We surveyed Fair A swine exhibitors and their household members. Confirmed cases had influenza-like illness (ILI) and a positive laboratory test for (H3N2)v, and probable cases had ILI. We calculated attack rates. We determined risk factors for infection, using multivariable log-binomial regression.

RESULTS

We identified 20 confirmed and 94 probable cases associated with Fair A. Among 114 cases, the median age was 10 years, there were no hospitalizations or deaths, and 82% had swine exposure. In the exhibitor household cohort of 359 persons (83 households), we identified 6 confirmed cases (2%) and 40 probable cases (11%). An age of <10 years was a significant risk factor (P < .01) for illness. One instance of likely human-to-human transmission was identified.

CONCLUSIONS

In this (H3N2)v outbreak, no evidence of sustained human-to-human (H3N2)v transmission was found. Our risk factor analysis contributed to the development of the recommendation that people at increased risk of influenza-associated complications, including children aged <5 years, avoid swine barns at fairs during the 2012 fair season.

Influenza A Virus Shedding and Infectivity in Households

BACKGROUND

Viral shedding is often considered to correlate with the infectivity of influenza, but the evidence for this is limited.

METHODS

In a detailed study of influenza virus transmission within households in 2008-2012, index case patients with confirmed influenza were identified in outpatient clinics, and we collected nose and throat swab specimens for testing by reverse-transcription polymerase chain reaction from all household members regardless of illness. We used individual-based hazard models to characterize the relationship between viral load (V) and infectivity.

RESULTS

Assuming that infectivity was proportional to viral load V gave the worst fit, because it strongly overestimated the proportion of transmission occurring at symptom onset. Alternative models assuming that infectivity was proportional to a various functions of V provided better fits, although they all overestimated the proportion of transmission occurring >3 days after symptom onset. The best fitting model assumed that infectivity was proportion to V(γ), with estimates of γ = 0.136 and γ = 0.156 for seasonal influenza A(H1N1) and A(H3N2) respectively.

CONCLUSIONS

All the models we considered that used viral loads to approximate infectivity of a case imperfectly explained the timing of influenza secondary infections in households. Identification of more accurate correlates of infectivity will be important to inform control policies and disease modeling.

Zanamivir versus trivalent split virus influenza vaccine: a pilot randomized trial

BACKGROUND

Healthcare workers may be exposed to people with respiratory viral infections more often than other working adults. Understanding the risk and the effectiveness of different preventive measures is of great importance.

OBJECTIVES

To estimate adherence to prophylactic antiviral medication for a full influenza season, to the compare efficacy of antiviral prophylaxis to that of the seasonal influenza vaccine and to identify exposures that increase risk of acute respiratory illnesses (ARI) in healthy adults.

METHODS

Participants were randomized 1:2 to receive the 2008-2009 influenza vaccine or daily prophylaxis with 10 mg of zanamivir during the season. Web-based questionnaires collected information on demographics, symptoms, exposures, medication use and side effects.

RESULTS

Sixty-four healthy adults were recruited in November 2008. Three of 40 active participants discontinued zanamivir due to side effects; the remaining 37 took >85% of scheduled doses for a median of 121 days. Symptomatic, laboratory-confirmed influenza was detected in one person randomized to zanamivir (2·5%) and 2/20 (10%) who received the vaccine (P = 0·25). Forty-seven participants reported 109 episodes of ARI. Factors associated with an ARI were exposure to a spouse (OR 7·2), child (OR 2·4) or patient (OR 2·0) with symptoms of an ARI in the previous 7 days.

CONCLUSIONS

Breakthrough influenza infection occurred in both vaccinated participants and those receiving antiviral prophylaxis. Most adults were willing and able to comply with season-long prophylaxis. Report of recent exposure to family members and patients with an ARI increased the risk of developing an ARI in healthy adults.

Viable influenza A virus in airborne particles from human coughs

Patients with influenza release aerosol particles containing the virus into their environment. However, the importance of airborne transmission in the spread of influenza is unclear, in part because of a lack of information about the infectivity of the airborne virus. The purpose of this study was to determine the amount of viable influenza A virus that was expelled by patients in aerosol particles while coughing. Sixty-four symptomatic adult volunteer outpatients were asked to cough 6 times into a cough aerosol collection system. Seventeen of these participants tested positive for influenza A virus by viral plaque assay (VPA) with confirmation by viral replication assay (VRA). Viable influenza A virus was detected in the cough aerosol particles from 7 of these 17 test subjects (41%). Viable influenza A virus was found in the smallest particle size fraction (0.3 μm to 8 μm), with a mean of 142 plaque-forming units (SD 215) expelled during the 6 coughs in particles of this size. These results suggest that a significant proportion of patients with influenza A release small airborne particles containing viable virus into the environment. Although the amounts of influenza A detected in cough aerosol particles during our experiments were relatively low, larger quantities could be expelled by influenza patients during a pandemic when illnesses would be more severe. Our findings support the idea that airborne infectious particles could play an important role in the spread of influenza.