Traditional definition of healthcare-associated influenza underestimates cases associated with other healthcare exposures in a population-based surveillance system

OBJECTIVE

To provide comprehensive population-level estimates of the burden of healthcare-associated influenza.

DESIGN

Retrospective cross-sectional study.

SETTING

US Influenza Hospitalization Surveillance Network (FluSurv-NET) during 2012-2013 through 2018-2019 influenza seasons.

PATIENTS

Laboratory-confirmed influenza-related hospitalizations in an 8-county catchment area in Tennessee.

METHODS

The incidence of healthcare-associated influenza was determined using the traditional definition (ie, positive influenza test after hospital day 3) in addition to often underrecognized cases associated with recent post-acute care facility admission or a recent acute care hospitalization for a noninfluenza illness in the preceding 7 days.

RESULTS

Among the 5,904 laboratory-confirmed influenza-related hospitalizations, 147 (2.5%) had traditionally defined healthcare-associated influenza. When we included patients with a positive influenza test obtained in the first 3 days of hospitalization and who were either transferred to the hospital directly from a post-acute care facility or who were recently discharged from an acute care facility for a noninfluenza illness in the preceding 7 days, we identified an additional 1,031 cases (17.5% of all influenza-related hospitalizations).

CONCLUSIONS

Including influenza cases associated with preadmission healthcare exposures with traditionally defined cases resulted in an 8-fold higher incidence of healthcare-associated influenza. These results emphasize the importance of capturing other healthcare exposures that may serve as the initial site of viral transmission to provide more comprehensive estimates of the burden of healthcare-associated influenza and to inform improved infection prevention strategies.

Patient influenza vaccination reduces the risk of hospital-acquired influenza: An incident test negative-case control study in Lyon university hospital, France (2004-2020)

BACKGROUND

Literature is limited on the impact of patient vaccination on the risk of hospital-acquired influenza (HAI). This test negative case-control study nested in a surveillance program aimed at evaluating the effectiveness of influenza vaccination in reducing the risk of HAI in hospitalized patients during 15 influenza seasons (2004-05 to 2019-20).

METHODS

HAI cases were those who developed influenza like illness (ILI) symptoms at least 72 h after hospitalization and had a positive reverse transcriptase-polymerase chain reaction (RT-PCR). Controls were those with ILI symptoms and a negative RT-PCR test. A nasal swab as well as socio-demographic, clinical data and information on influenza vaccination were collected.

RESULTS

Of the 296 patients included, 67 were confirmed HAI cases. Influenza vaccine coverage was significantly higher among controls compared to HAI cases (p = 0.002). The risk of HAI was reduced by almost 60 % in vaccinated patients.

CONCLUSIONS

A better control of HAI can be achieved by vaccinating hospitalized patients.

Effect of a multimodal strategy for prevention of nosocomial influenza: a retrospective study at Grenoble Alpes University Hospital from 2014 to 2019

Background

A multimodal strategy to prevent nosocomial influenza was implemented in 2015–2016 in Grenoble Alpes University Hospital. Three modalities were implemented in all units: promotion of vaccination among healthcare workers, epidemiologic surveillance and communication campaigns. Units receiving a high number of patients with influenza implemented 2 additional modalities: improvement of diagnosis capacities and systematic surgical mask use. The main objective was to assess the effectiveness of the strategy for reducing the risk of nosocomial influenza.

Methods

A study was conducted retrospectively investigating 5 epidemic seasons (2014–2015 to 2018–2019) including all patients hospitalized with a positive influenza test at Grenoble Alpes University Hospital. The weekly number of nosocomial influenza cases was analyzed by Poisson regression and incidence rate ratios (IRR) were estimated.

Results

A total of 1540 patients, resulting in 1559 stays, were included. There was no significant difference between the 5 influenza epidemic seasons in the units implementing only 3 measures. In the units implementing the 5 measures, there was a reduction of nosocomial influenza over the seasons when the strategy was implemented compared to the 2014–2015 epidemic season (IRR = 0.56, 95% CI = 0.23–1.34 in 2015–2016; IRR = 0.39, 95% CI = 0.19–0.81 in 2016–2017; IRR = 0.50, 95% CI = 0.24–1.03 in 2017–2018; IRR = 0.48, 95% CI = 0.23–0.97 in 2018–2019).

Conclusions

Our data mainly suggested that the application of the strategy with 5 modalities, including systematic surgical mask use and rapid diagnosis, seemed to reduce by half the risk of nosocomial influenza. Further data, including medico-economic studies, are necessary to determine the opportunity of extending these measures at a larger scale.

Is it possible to hospitalize patients in multiple-bed room without increasing the risk of hospital-acquired influenza? Description of a pragmatic preventive strategy in a French university hospital

BACKGROUND

Large inrush of patients through Emergency Department during influenza season can be dramatic. The purpose of this study was to evaluate the impact of an emergency preventive strategy, namely admission of patients with influenza in multiple-bed room with patients free from influenza, on the occurrence of hospital-acquired influenza (HAI).

METHODS

When a patient with an influenza RT-PCR diagnosis was hospitalized in a multiple-bed room, the emergency preventive strategy was applied: selection of non-immunocompromised neighbor, implementation of physical barriers (rigid screen pulled between beds, surgical mask for healthcare workers and visitors), preemptive Oseltamivir therapy for the neighbor.

RESULTS

From 29/11/2017 to 10/05/2018 a total of 464 hospitalized influenza patients were included; 318 were placed in multiple-bed room and 141 in single room. Emergency preventive strategy was correctly applied for 75.1% of patients in multiple-bed room. A total of 8 exposed neighbors matched HAI definition despite strategy. 7 were already exposed to the case before the set-up of the strategy. Only one case of documented transmission of influenza occurred after application of an incorrect emergency preventive strategy: preventive posology of Oseltamivir was not correct.

CONCLUSIONS

These preliminary results suggest that the occurrence of HAI in multiple-bed rooms can be limited by the implementation of maximum precautions and urge us to promote further evaluation of the strategy. A detection bias should be considered without a systematic neighbors monitoring.

Incidence of Asymptomatic and Symptomatic Influenza Among Healthcare Workers: A Multicenter Prospective Cohort Study

BACKGROUND

Influenza is an important cause of viral hospital-acquired infection involving patients, healthcare workers (HCW), and visitors. The frequency of asymptomatic influenza among HCW with possible subsequent transmission is poorly described. The objective is to determine the cumulative incidence of asymptomatic, paucisymptomatic, and symptomatic influenza among HCW.

METHOD

A multicenter prospective cohort study was done in 5 French university hospitals, including 289 HCW during the 2016-2017 influenza season. HCW had 3 physical examinations (time [T] 0, before epidemic onset; T.1, before epidemic peak; T.2, T.3, after epidemic peak). A blood sample was taken each time for influenza serology and a nasal swab was collected at T1 and T2 for influenza detection by polymerase chain reaction (PCR). Positive influenza was defined as either a positive influenza PCR, and/or virus-specific seroconversion against influenza A, the only circulating virus, with no vaccination record during follow-up. Symptoms were self-reported daily between T1 and T2. Cumulative incidence of influenza was stratified by clinical presentation per 100 HCW.

RESULTS

Of the 289 HCW included, 278 (96%) completed the entire follow-up. Overall, 62 HCW had evidence of influenza of whom 46.8% were asymptomatic, 41.9% were paucisymptomatic, and 11.3% were symptomatic. Cumulative influenza incidence was 22.3% (95% confidence interval [CI]: 17.4%-27.2%). Cumulative incidence of asymptomatic influenza was 5.8% (95% CI: 3.3%-9.2%), 13.7% (95% CI: 9.9%-18.2%) for paucisymptomatic influenza, and 2.9% (95% CI: 1.3%-5.5%) for symptomatic influenza.

CONCLUSIONS

Asymptomatic and paucisymptomatic influenza were frequent among HCW, representing 47% and 42% of the influenza burden, respectively. These findings highlight the importance of systematic implementation of infection control measures among HCW regardless of respiratory symptoms from preventing nosocomial transmission of influenza.

CLINICAL TRIALS REGISTRATION

NCT02868658.

Description of an influenza outbreak in a French university hospital and risk factors of nosocomial influenza

Our objective was to evaluate risk factors of nosocomial influenza (NI) in an university hospital during the 2015/2016 influenza season. All hospitalized patients with influenza-like illness associated with laboratory confirmation by polymerase chain reaction were included in a prospective observational study. We identified 44 cases (19%) of NI among the 233 cases of influenza: 38/178 (21%) in adults and 6/55 (11%) in children. Among adults, hospitalization in a double or multi-occupancy room was independently associated with NI (adjusted Odds Ratio, 3.42; 95% CI, 1.29-9.08; p = 0.013). The results of the study underline the importance of single room to prevent NI.

Risk factors and clinical characteristics of patients with nosocomial influenza A infection

Influenza is a public health burden, responsible for more than half a million deaths worldwide each year and explosive outbreaks in-hospital care units. At present, little is known about clinical characteristics and outcomes with nosocomial influenza infection. To assess clinical characteristics and outcome between nosocomial and community-acquired (CA) influenza in a tertiary care hospital. A retrospective study of hospitalized patients in a French tertiary care hospital from 1st December 2016 to 28th February 2017 for flu-illness confirmed by reverse transcription PCR. Overall, 208 patients with laboratory-confirmed influenza were included; whose 49 nosocomial cases (23.6%). Patients with nosocomial influenza were significantly older (79.1 ± 15.5 vs 64.8 ± 31.1 years old; P = .003), with the more rapidly fatal disease (10.2% vs 1.3%; P = .0032). They had a less respiratory failure (8.2% vs 21.4%; P = .036) but had a longer length of hospitalization (47.3 vs 12.9 days; P < .001) than patients with CA influenza. During this influenza outbreak, 19 patients died (9.1%), none of them were vaccinated. Effective control of outbreaks in hospital facilities is challenging. Hospitalized patients are vulnerable to nosocomial Influenza infections that can increase the length of stay and be responsible for the death. Surveillance and early warning systems should be encouraged. Vaccination policies in conjunction with isolation measures and better hand hygiene could reduce virus spreading in hospitals.

Nosocomial influenza: encouraging insights and future challenges

PURPOSE OF REVIEW

The prevalence and incidence of viral nosocomial influenza infections in healthcare settings are underestimated. Nosocomial influenza outbreaks are frequent, and control remains challenging in acute care and long-term healthcare settings. This review examines recent publications on the determinants of nosocomial influenza prevention and control.

RECENT FINDINGS

Nosocomial influenza outbreaks occur in various healthcare settings, especially among the frail and elderly. The correct diagnosis is commonly missed because a substantial proportion of asymptomatic cases can transmit infections. Rapid diagnosis will facilitate rapid identification of cases and the implementation of control measures but needs confirmation in some circumstances, such as the description of transmission chains. Links between patients and healthcare personnel (HCP) have been well explored by phylogenetic virus characterization and need additional refinement and study. The preventive role of HCP vaccination in influenza incidence among patients should be investigated further in various settings to take into account different strategies for vaccination (i.e. voluntary or mandatory vaccination policies). Indeed, in Europe, influenza vaccination remains modest, whereas in North America hospitals and some states and provinces are now mandating influenza vaccination among HCP. The variability of vaccine effectiveness by seasonal epidemics is also an important consideration for control strategies.

SUMMARY

When influenza cases occur in the community, the risk of transmission and nosocomial cases increase in healthcare settings requiring vigilance among staff. Surveillance and early warning systems should be encouraged. Outbreak control needs appropriate identification of cases and transmission chains, and rapid implementation of control measures. Vaccination policies in conjunction with appropriate infection control measures could reduce virus spreading in hospitals. HCP vaccination coverage must be improved.

Definition of healthcare-associated influenza: A review and results from an international survey

Aim

To describe definitions of healthcare‐associated influenza (HAI) in recent literature and in hospitals participating in a survey of Society for Healthcare Epidemiology of America (SHEA) Research Network (SRN) members.

Method

A review with PubMed search was undertaken to retrieve articles published between 2008 and 2016, focusing on the subject headings “influenza, human” and “cross infection.” Definitions of clinical influenza‐like illness (ILI) and HAI were identified. An invitation to participate in the survey was sent to 218 SRN members via email.

Results

Of 75 articles on HAI included in the review, 30 presented a standardized definition of clinical ILI based on fever (100%), cough (80%), and sore throat (70%). Forty studies (53%) contained a standardized HAI definition, grounded on threshold delay from admission in 29 of them, this delay ranging from 48 to 196 hour (median: 72 hour). Fifty‐five SRN members responded to the survey, with a standardized definition of HAI adopted by 76% of them. This definition was based on clinical features for 24%, virological features for 31%, and both for 45%. Fever (mean threshold: 38.0°C) was part of the definition for 82%. The features required most frequently in the clinical definition were cough (46%) and sore throat (26%). Median threshold delay between admission and symptoms onset adopted for HAI definition was 48 hour (range: 24‐96 hour).

Conclusion

This work underlined the heterogeneity of HAI definitions in different countries. A standardized definition would be helpful to evaluate HAI spread, outcomes in patients and healthcare systems, and the impact of prevention measures, including vaccination.

Influence of observable and unobservable exposure on the patient's risk of acquiring influenza-like illness at hospital

During outbreaks of hospital-acquired influenza-like illness (HA-ILI) healthcare workers (HCWs), patients, and visitors are each a source of infection for the other. Quantifying the effects of these various exposures will help improve prevention and control of HA-ILI outbreaks. We estimated the attributability of HA-ILI to: (1) exposure to recorded or unrecorded sources; (2) exposure to contagious patient or contagious HCW; (3) exposure during observable or unobservable contagious period of the recorded sources; and, (4) the moment of exposure. Among recorded sources, 59% [95% credible interval (CrI) 34-83] of HA-ILI of patients was associated with exposure to contagious patients and 41% (95% CrI 17-66) with exposure to contagious HCWs. Exposure during the unobservable contagiousness period of source patients accounted for 49% (95% CrI 19-75) of HA-ILI, while exposure during the unobservable contagiousness period of source HCWs accounted for 82% (95% CrI 51-99) of HA-ILI. About 80% of HA-ILIs were associated with exposure 1 day earlier. Secondary cases of HA-ILI might appear as soon as the day after the detection of a primary case highlighting the explosive nature of HA-ILI spread. Unobservable transmission was the main cause of HA-ILI transmission suggesting that symptom-based control measures alone might not prevent hospital outbreaks. The results support the rapid implementation of interventions to control influenza transmission.

Hospitalization in double-occupancy rooms and the risk of hospital-acquired influenza: a prospective cohort study

Hospitalization in double-occupancy rooms and the risk of hospital-acquired influenza were assessed prospectively. The incidence was 2.0 for 100 patient-days in double- vs. 0.7 in single-occupancy rooms (p 0.028). The adjusted hazard ratio of hospital-acquired influenza was 2.67 (95% confidence interval 1.05-6.76) in patients hospitalized in double- compared to single-occupancy rooms.

Characterisation of nosocomial and community-acquired influenza in a large university hospital during two consecutive influenza seasons

BACKGROUND

Nosocomial influenza is increasingly recognized as an important public health threat causing considerable morbidity and mortality each year. However, data on nosocomial influenza is usually collected during outbreaks only and clinical information of nosocomial influenza is sparsely available.

OBJECTIVES

To systematically analyse the distribution of nosocomial and community-acquired influenza and epidemiological characteristics in a tertiary care unit in two consecutive seasons.

STUDY DESIGN

A retrospective observational study was conducted to identify and characterise cases of nosocomial and community-acquired influenza at Freiburg University hospital from 1 January 2013 to 30 April 2014. A validated multiplex RT-PCR to detect influenza virus and other respiratory pathogens was used throughout. Clinical information was retrieved from the hospital-based information system.

RESULTS

Overall, 218 patients with laboratory-confirmed influenza were included (179 in the first, 39 patients in the second season). A rate of 20% of nosocomial influenza was observed throughout. A fatal outcome was recorded for 9% of nosocomial cases, which were mainly associated with influenza virus A(H1N1)pdm09. Nosocomial influenza occurred in all age groups, but fatalities were only observed in patients ≥18 years. Patients with nosocomial influenza were significantly older, underwent therapy for blood malignancies and immunosuppressive regimens more frequently, and received solid organ transplantation more often compared to community-acquired patients.

CONCLUSIONS

Despite the different distribution of virus subtypes and epidemiological properties between both influenza seasons, the rate of nosocomial cases remained similar. Systematic detection and targeted prevention measures seem mandatory to minimize nosocomial influenza.