Oseltamivir Prophylaxis Research Articles

Oseltamivir for the Prevention of Influenza in Residents of Long-Term Care Facilities


 The clinical effectiveness of oseltamivir for the prevention of influenza in residents of long-term care facilities compared to no prophylaxis is unclear. The evidence we identified is inconclusive due to limitations in the quality of studies.
 We did not find any evidence on the safety of oseltamivir for preventing influenza in long-term care facilities.
 We did not find any studies on the clinical effectiveness or safety of oseltamivir prophylaxis in long-term care facilities compared to placebo.

Neuraminidase inhibitors for treatment of influenza.

Neuraminidase inhibitors (NAIs) are commonly used in the prevention and treatment of influenza. Previous studies and reviews have demonstrated a questionable and modest benefit of their use while demonstrating potential adverse effects.1,2.

Antiviral prophylaxis is effective in reducing influenza outbreak severity in residential care

Background: Influenza outbreaks in aged care facilities (ACFs) can lead to hospitalisations and deaths. Influenza can spread rapidly through ACFs if precautionary measures are not taken. Along with the influenza vaccination and precautionary hygiene measures, oseltamivir may be effective in reducing the attack rate of influenza. Methods and materials: Administrative data with enhanced surveillance of influenza outbreaks was used to investigate the effectiveness of oseltamivir prophylaxis use during influenza outbreaks in ACF located within South Western Sydney Local Health District from 1st January 2015 to December 31st 2018. The key outcome variable was the rate of seroconversion after receiving oseltamivir. Subgroups and various predictors of oseltamivir seroconversion were investigated including presence of a dementia ward, high care ward, strain of influenza, vaccination rates (staff and patients) and days to Public Health Unit (PHU) notification. Results: The cohort consisted of 86 ACF outbreaks involving 10,064 patients. Oseltamivir prevented 90% of influenza cases during influenza outbreaks. (0.1RR (95%CI: 0.0804–0.1248; p < 0.0001)). ACFs with dementia wards had a 44% (0.56RR (95%CI: 0.34–0.93); p < 0.05) lower oseltamivir seroconversion rate. ACFs with high level care had an 86% (0.13RR (95%CI: 0.05–0.38); p < 0.05) lower oseltamivir seroconversion rate. For each day delay in the ACF notifying the PHU of the influenza outbreak there was a 4% increase in the rate of deaths and 4% increase in hospitalisations among residents. For each day delay in notifying the PHU the duration of the outbreak was extended by 0.42 days. ACFs with only high care wards had 29% less clinical cases. The seroconversion rate was 87% lower in the high care ACFs indicating oseltamivir was more effective in the high care setting. Despite this, the rates of oseltamivir prescription was the same in high care only ACFs vs. other ACFs. There were 34% less clinical cases and 66% less hospitalisations in wards with influenza B compared with influenza A. Conclusion: Oseltamivir prophylaxis is highly effective in preventing new cases of influenza during outbreaks in ACFs, especially in facilities with dementia or high care wards. Mandatory reporting of influenza outbreaks in ACFs to PHUs will further assist in reducing hospitalisation, mortality and duration of outbreak.

Oseltamivir-Induced Neuropsychiatric Event in an Older Person: A Case Report

BACKGROUND: Oseltamivir is an effective agent for both the treatment and prevention of influenza, and its use is increasing. The package insert indicates that delirium and delirium-like events have been reported with the use of oseltamivir during postmarketing surveillance. The reports of neuropsychiatric events associated with oseltamivir are mainly in younger patients. To our knowledge, this is the first reported case of oseltamivirassociated neuropsychiatric events occurring with oseltamivir prophylaxis in an older adult.<br/> CASE PRESENTATION: A 74-year-old male with a history of mild neurocognitive disorder was given oseltamivir prophylaxis in the setting of an influenza outbreak during his rehabilitation facility stay and developed newfound psychiatric symptoms after administration of oseltamivir for influenza prophylaxis because of institutional outbreak. The patient recovered completely after cessation of oseltamivir.<br/> CONCLUSION: We hope that our case report highlights the importance of careful consideration when prescribing oseltamivir prophylaxis in older people with or without previous history of neurocognitive disorder.

Effectiveness of Oseltamivir Prophylaxis in Influenza Outbreaks in Residential Aged Care

Influenza outbreaks in Aged Care Facilities (ACFs) can lead to hospitalizations and deaths. Influenza can spread rapidly through ACFs if precautionary measures are not taken. Along with influenza vaccination and precautionary hygiene measures, Oseltamivir Prophylaxis (OP) may be effective in reducing the attack rate of influenza by preventing new cases. A cohort study was carried out to investigate the effectiveness of OP use during influenza outbreaks in ACFs located within South Western Sydney Local Health District from 1 January 2015 to 31 December 2018. The main outcome assessed was the rate of OP failure (new cases of influenza in patients treated with OP) among ACF residents. Subgroups and various predictors of OP failure were investigated including presence of a dementia ward, high care ward, and days to Public Health Unit (PHU) notification. The cohort consisted of 86 ACF outbreaks involving 10,064 residents. OP prevented 90% of influenza cases during influenza outbreaks [0.1 RR (95% confidence interval (CI): 0.08–0.12); P < 0.0001]. ACFs with dementia wards had a 44% (0.56 relative risk (RR) (95% CI: 0.34–0.93); P < 0.05) lower OP failure rate. ACFs with high level care had an 87% (0.13 RR (95% CI: 0.05–0.38); P < 0.05) lower OP failure rate. OP is highly effective in preventing new cases of influenza during outbreaks in ACFs, especially in ACFs with dementia or high care wards. Mandatory reporting of influenza outbreaks to PHUs would ensure that ACFs are supported throughout the outbreak, which will facilitate reductions in hospitalizations and mortality.

Impact of prophylactic oseltamivir on INR in patients on stable warfarin therapy.

Influenza prophylaxis with oseltamivir is recommended for exposed high-risk patients. Patients with many comorbidities have an increased likelihood of co-administration of oseltamivir and warfarin. Evidence of a drug interaction is conflicting in the literature and is limited to a 5-day treatment course. This study evaluates the impact of prophylactic oseltamivir on international normalized ratio (INR) in patients taking warfarin. This retrospective cohort study conducted within the Veterans Health Administration included patients on warfarin who received oseltamivir for influenza prophylaxis. The primary endpoint was change in INR from baseline to day 10 of oseltamivir treatment. Secondary endpoints included change in INR based on renal function and duration of oseltamivir prophylaxis, trend in INR, and frequency of bleeding and thrombosis events. A total of 1041 patients were included and received oseltamivir for a mean of 12.9days. The mean post-oseltamivir INR was significantly increased compared to the pre-oseltamivir INR (2.39 to 2.52; p < 0.001). Patients with a creatinine clearance of 31-60mL/min had a significant increase in INR (2.40 to 2.59; p < 0.01). There was an increase in INR when oseltamivir was used for 7 or 8-10days. Of included patients, 5.1% and 1.8% had a recorded thrombosis or bleeding event, respectively. There was a significant increase in INR in patients on chronic warfarin therapy and concomitant prophylactic oseltamivir, but this change may only be clinically significant for certain patient populations. The most impact on INR was within 7-10days of oseltamivir initiation and in patients with impaired renal function.

Postexposure prophylaxis with oseltamivir in outbreak control of pH1N1 influenza onboard a naval warship: An observational study

Background: Control measures such as maintenance of social distancing, hand hygiene, respiratory hygiene, regular disinfection, and keeping a high index of suspicion for probable cases form the basis of containing a pH 1N1 outbreak onboard a Naval ship. As per the present guidelines, though a quadrivalent vaccine is recommended for health-care workers in close contact, anti-flu postexposure prophylaxis strategies have been predicted to be effective in some mathematical models. Chemoprophylaxis with oseltamivir was assumed to be an effective measure to control the outbreak onboard ship while at sea. Materials and Methods: A total of 275 asymptomatic individuals were started on oral oseltamivir prophylaxis on board from day 17 onward for a duration of 10 days and side effects of the medication were noted. Results: With chemoprophylaxis of the entire crew with oseltamivir, the number of positive cases per day reduced. The outbreak cleared within 3 days of initiation of chemoprophylaxis. Active surveillance was continued for 14 days since the last positive case. Conclusion: In an afloat setting, with a rapidly spreading outbreak of airborne disease, mass chemoprophylaxis with oral oseltamivir along with aggressive public health control measures were found to have contained the spread with only mild side effects which were reported.

Nosocomial outbreak of influenza A H3N2 in an inpatient oncology unit related to health care workers presenting to work while ill

ObjectiveTo describe an outbreak of influenza A in an oncology unit, highlighting infection control methods implemented, and examining reasons health care workers (HCWs) present to work with influenza-like illness (ILI).MethodsConfirmed cases were defined by the presence of ILI and a positive nasopharyngeal polymerase chain reaction swab for influenza A H3. Probable cases were defined as exposed HCWs with ILI who were unavailable for polymerase chain reaction testing. Infection prevention measures included closing the ward for new admissions, oseltamivir prophylaxis for all exposed groups, and dismissal from work of HCWs with ILI until resolution of symptoms. An anonymous survey of the cases in our HCWs was conducted to better elucidate reasons behind presenteeism.ResultsOver the course of 8 days (November 16, 2017, to November 22, 2017), influenza was diagnosed in 7 of 10 inpatients on the oncology ward, 16 HCWs (14 confirmed, 2 probable), and 2 visitors. The suspected index case was an HCW. Of the surveyed HCWs, 64% presented to work despite feeling ill (ie, presenteeism). The most common reason was “sense of duty as a health care worker.”ConclusionsThis nosocomial outbreak of influenza highlights the challenges of protecting inpatients from viral respiratory tract infections. HCWs and patient visitors with ILI should avoid work or visiting until resolution of peak respiratory symptoms and adhere to strict respiratory etiquette.

688. Impact of Expanded Influenza Post-exposure Prophylaxis on Healthcare Worker Absenteeism at a Tertiary Care Center During the 2017–2018 Season

BackgroundA severe 2017–2018 influenza season was expected for the United States. We hypothesized that a surge in influenza cases paired with decreased vaccine effectiveness could increase healthcare worker (HCW) absenteeism. Because of a potential public health emergency during the 2017–2018 season, we offered oseltamivir post-exposure prophylaxis (PEP) to exposed HCWs regardless of vaccination status. We describe PEP uptake, cost, and impact on absenteeism at the University of Iowa Hospital and Clinics (UIHC).MethodsUIHC serves as a referral and safety net health system for Eastern Iowa. Influenza seasons were defined as the period between Week 40 from 1 year to Week 13 of the following year. During the 2016–2017 season, PEP (75 mg/day for 7 days) was offered free of charge to unvaccinated exposed HCWs. Exposure was defined as proximity within 3 ft of a confirmed influenza-infected person for ≥10 minutes without mask protection, or direct contact with respiratory secretions. During the 2017–2018 season, PEP was expanded to all exposed HCWs regardless of vaccination status. We reviewed surveillance, employee health, pharmacy, and human resources records for the 2016–2017 and 2017–2018 seasons. We defined PEP uptake as prescriptions picked up/all referrals and absenteeism rate as sick-leave requests/scheduled hours.ResultsDuring the 2016–2017 and 2017–2018 seasons, we detected 373 and 427 confirmed influenza cases among patients at UIHC. HCW vaccination rates were similar: 89.7% and 90.9%. PEP was recommended in 49 exposures during 2016–2017 and 280 exposures during 2017–2018. A total of 22 (44.9%) and 133 (47.5%) HCWs picked up oseltamivir from the pharmacy during the 2016–2017 and 2017–2018 seasons. The estimated cost of oseltamivir was $1,791 and $10,828, respectively. Overall, 6,187 sick-leave requests (median = 12 hours, absenteeism rate = 3.2%), and 6,174 sick-leave requests (median = 12 hours, absenteeism rate = 3.4%) were reported during the 2016–2017 and 2017–2018 seasons.ConclusionInfluenza case counts mildly increased from the 2016–2017 to the 2017–2018 season. Expanding PEP to all exposed HCWs, regardless of vaccination status, had moderate uptake and was costly. Absenteeism rates remained similar during both seasons.Disclosures All authors: No reported disclosures.

1159. Influenza Symptoms in Vaccinated Healthcare Workers in an H3N2-Dominant Season

BackgroundInfluenza vaccination of healthcare workers is an important component of keeping patients safe, but must be paired with exclusion of ill healthcare workers (HCW) from work. CDC recommends exclusion from work until afebrile for 24 hours, but not all HCW with influenza develop fever and may still be a risk for spreading. Half of HCW with influenza in an H1N1-dominant season (2013–2014) at our institution were afebrile.MethodsFrom 1/31–4/24/18 (H3N2-dominant season), HCW with fever or cough were screened for influenza and respiratory syncytial virus by polymerase chain reaction of flocked nasopharyngeal swabs. Additional HCW were tested by their primary care providers. We collected influenza vaccination status and symptoms and calculated the proportion of influenza-positive HCWs with fever or cough. Infection control practitioners (ICPs) contacted each influenza-positive HCW to identify potential patient or HCW exposures 24 hours prior to symptom onset and offered oseltamivir prophylaxis to exposed patients and HCW.ResultsOf 186 HCW tested by UCM, 49 (26%) tested positive for influenza (35 with influenza A; 14 with influenza B) and 11 (6%) tested positive for RSV. Forty-eight HCW (98%) received influenza vaccination. Fever was reported in only 19 (54%) HCW with influenza A and three (21%) HCW with influenza B. Cough was present in the majority of HCW (34 (97%) with influenza A and 12 (86%) with influenza B). An additional 55 HCW were diagnosed with influenza by their primary care providers. ICPs performed contact investigations for 43 HCW who reported exposure to patients or other HCW between 24 hours before symptom onset through the time of diagnosis. Occupational medicine provided 138 courses of prophylactic oseltamivir to HCW.ConclusionAfebrile influenza illness is common; current workforce guidelines are insufficient to prevent exposure in the healthcare setting. Expanding employee influenza screening to include fever OR cough doubled the number influenza positive HCW identified. Despite excellent influenza vaccination rates, vigilance is critical to prevent influenza transmission in the hospital. HCW screening for influenza based on fever OR cough, exclusion from work, and identification of potential exposures can help keep patients and colleagues safe.Disclosures All authors: No reported disclosures.

Safety and effectiveness of neuraminidase inhibitors for influenza treatment, prophylaxis, and outbreak control: a systematic review of systematic reviews and/or meta-analyses.

To review evidence from systematic reviews and/or meta-analyses (SR/MAs) regarding neuraminidase inhibitor (NI) safety and effectiveness. We conducted an SR of SR/MAs of randomized control and/or observational studies. We searched eight electronic databases for SR/MAs that examined the effectiveness or safety of NIs administered for influenza (i.e. influenza-like illness or lab-confirmed) treatment or prophylaxis. We identified 27 (0.7%) eligible SR/MAs of 3723 articles reviewed. NI (n = 2) or oseltamivir (n = 1) versus no treatment were consistently associated with a decrease in mortality odds among the hospitalized, general population (OR range 0.2 - 0.8). Oseltamivir versus no treatment was associated with a decrease in hospitalization and pneumonia risk/odds in 2/4 SR/MAs. Oseltamivir (n = 4) and zanamivir (n = 3) were consistently associated with a 0.5 - 1 day decrease in symptom duration. Oseltamivir (n = 4) or zanamivir (n = 4) versus no prophylaxis were consistently associated with a decrease in the odds/risk of symptomatic secondary transmission (OR/RR range 0.1 - 0.5). Oseltamivir versus no treatment was consistently associated with a 1.5- to 2.5-fold increase in the odds/risk of nausea (n = 4) and vomiting (n = 5). NI treatment is likely to be effective at reducing mortality among hospitalized patients, and symptom duration by up to 1 day in the general population. Oseltamivir or zanamivir prophylaxis are likely to be effective at reducing secondary symptomatic influenza transmission. Increased nausea and vomiting are likely associated with oseltamivir use. We recommend that decisions regarding NI use are made in consideration of potential adverse events, particularly for the general population at low risk of complications. Among hospitalized patients, NI administration seems warranted to reduce mortality risk.

Combined interventions for mitigation of an influenza A (H1N1) 2009 outbreak in a physical training camp in Beijing, China

Many studies have suggested the effectiveness of single control measures in the containment and mitigation of pandemic influenza A (H1N1) 2009. The effects of combined interventions by multiple control measures in reducing the impact of an influenza A (H1N1) 2009 outbreak in a closed physical training camp in Beijing, China were evaluated. Oseltamivir was prescribed for the treatment of confirmed cases and possible cases and as prophylaxis for all other participants in this training camp. Public health control measures were applied simultaneously, including the isolation of patients and possible cases, personal protection and hygiene, and social distancing measures. Symptom surveillance of all participants was initiated, and the actual attack rate was calculated. For comparison, the theoretical attack rate for this outbreak was projected using the Newton-Raphson numerical method. A total of 3256 persons were present at the physical training camp. During the outbreak, 405 (68.3%) possible cases and 26 (4.4%) confirmed cases were reported before the intervention and completed oseltamivir treatment; 162 (27.3%) possible cases were reported after the intervention and received part treatment and part prophylaxis. The other 2663 participants completed oseltamivir prophylaxis. Of the possible cases, 181 with fever ≥38.5°C were isolated. The actual attack rate for this outbreak of pandemic influenza A (H1N1) 2009 was 18.2%, which is much lower than the theoretical attack rate of 80% projected. Combined interventions of large-scale antiviral ring prophylaxis and treatment and public health control measures could be applied to reduce the magnitude of influenza A (H1N1) 2009 outbreaks in closed settings.

Influenza Prophylaxis in Children: Could a Single Dose of One Drug Be an Option?

During annual influenza epidemics, the highest illness rates occur among children, who are also known to play substantial roles in influenza transmission among households and communities. The Centers for Disease Control and Prevention recommend postexposure chemoprophylaxis with neuraminidase inhibitors for close contacts at elevated risk for influenza complications who have not been vaccinated or are unlikely to be protected through vaccination or other contact precautions at the time of exposure.1 The effectiveness of postexposure prophylaxis with neuraminidase inhibitors is estimated to be 68% to 90%. The American Academy of Pediatrics recommends oral oseltamivir prophylaxis in infants starting at 3 months of age and in high-risk children, and inhaled zanamivir prophylaxis is recommended only in children ≥5 years old.1,2 Intravenous peramivir is not approved for children or for prophylaxis in the United States. The recommended duration of prophylaxis currently is 7 to 10 days from last exposure or … Address correspondence to Flor M. Munoz, MD, FAAP, Associate Professor of Pediatrics, Molecular Virology and Microbiology, Baylor College of Medicine, One Baylor Plaza, BCM-280, Houston, TX 77030. E-mail: florm{at}bcm.edu

Successful use of oseltamivir prophylaxis in managing a nosocomial outbreak of influenza A in a hematology and allogeneic stem cell transplant unit.

To describe a nosocomial outbreak of H1N1 influenza A in an inpatient hematology and allogeneic stem cell transplant unit and outcomes of universal oseltamivir prophylaxis. Medical records of all patients admitted to the unit were reviewed to define the nosocomial outbreak, commencing 1 week prior to the index case until 4 weeks following institution of oseltamivir prophylaxis. Timelines for clinical symptoms, viral spread, management, patient outcomes and follow up testing were constructed. All cases of influenza were confirmed on nasopharyngeal swabs and/or bronchoalveolar lavages collected for polymerase chain reaction testing. In addition to the index case, further 11 patients were diagnosed with influenza A during the outbreak. Six patients (50%) had influenza-like-illness, five (42%) had respiratory symptoms only and one (8%) was asymptomatic. In total, five patients died, including four (33%) patients who were admitted to intensive care. A clustering of seven cases led to recognition of the outbreak and subsequent commencement of universal prophylaxis with oseltamivir 75 mg/day in all inpatients within the unit. Strict infection control processes were reinforced concurrently. There were no further cases of influenza A linked to the outbreak after the implementation of universal oseltamivir prophylaxis. Three later cases were linked to H1N1 exposure during the original outbreak. H1N1 influenza infection is associated with significant mortality in hematology patients. Universal prophylaxis with oseltamivir during a nosocomial outbreak appeared to be effective in controlling spread of the virus. We recommend early institution of infection control and universal prophylaxis in any nosocomial outbreak of influenza.

Evaluation of the use of oseltamivir prophylaxis in the control of influenza outbreaks in long-term care facilities in Alberta, Canada: a retrospective provincial database analysis

ObjectivesTo evaluate the impact of oseltamivir prophylaxis in the management and control of influenza outbreaks in long-term care facilities in Alberta, Canada.Setting and participantsLong-term care facilities where 127 influenza outbreaks...

Neuraminidase inhibitors for influenza: a systematic review and meta-analysis of regulatory and mortality data.

Neuraminidase inhibitors (NIs) are stockpiled and recommended by public health agencies for treating and preventing seasonal and pandemic influenza. They are used clinically worldwide. To (1) describe the potential benefits and harms of NIs for influenza in all age groups by reviewing all clinical study reports (CSRs) of published and unpublished randomised, placebo-controlled trials and regulatory comments; and (2) determine the effect of oseltamivir (Tamiflu(®), Roche) treatment on mortality in patients with 2009A/H1N1 influenza. We searched trial registries, electronic databases and corresponded with regulators and sponsors to identify randomised trials of NIs. We requested full CSRs and accessed regulators' comments. We included only those trials for which we had CSRs. To examine the effects of oseltamivir on 2009A/H1N1 influenza mortality, we requested individual patient data (IPD) from corresponding authors of all included observational studies. Effect of oseltamivir and zanamivir (Relenza®, GlaxoSmithKline) in the prevention and treatment of influenza: Oseltamivir reduced the time to first alleviation of symptoms in adults by 16.8 hours [95% confidence interval (CI) 8.4 to 25.1 hours]. Zanamivir reduced the time to first alleviation of symptoms in adults by 0.60 days (95% CI 0.39 to 0.81 days). Oseltamivir reduced unverified pneumonia in adult treatment [risk difference (RD) 1.00%, 95% CI 0.22% to 1.49%]; similar findings were observed with zanamivir prophylaxis in adults (RD 0.32%, 95% CI 0.09% to 0.41%). Oseltamivir treatment of adults increased the risk of nausea (RD 3.66%, 95% CI 0.90% to 7.39%) and vomiting (RD 4.56%, 95% CI 2.39% to 7.58%). In the treatment of children, oseltamivir induced vomiting (RD 5.34%, 95% CI 1.75% to 10.29%). Both oseltamivir and zanamivir prophylaxis reduced the risk of symptomatic influenza in individuals (oseltamivir RD 3.05%, 95% CI 1.83% to 3.88%; zanamivir RD 1.98%, 95% CI 0.98% to 2.54%) and in households (oseltamivir RD 13.6%, 95% CI 9.52% to 15.47%; zanamivir RD 14.84%, 95% CI 12.18% to 16.55%). Oseltamivir increased psychiatric adverse events in the combined on- and off-treatment periods (RD 1.06%, 95% CI 0.07% to 2.76%) and the risk of headaches while on treatment (RD 3.15%, 95% CI 0.88% to 5.78%). Effect of oseltamivir on mortality in patients with 2009A/H1N1 influenza: Analysis of summary data of 30 studies as well as IPD of four studies showed evidence of time-dependent bias. After adjusting for time-dependent bias and potential confounding variables, competing risks analysis of the IPD showed insufficient evidence that oseltamivir reduced the risk of mortality (hazard ratio 1.03, 95% CI 0.64 to 1.65). Oseltamivir and zanamivir cause small reductions in the time to first alleviation of influenza symptoms in adults. The use of oseltamivir increases the risk of nausea, vomiting, psychiatric events in adults and vomiting in children. Oseltamivir has no protective effect on mortality among patients with 2009A/H1N1 influenza. Prophylaxis with either NI may reduce symptomatic influenza in individuals and in households. The balance between benefits and harms should be considered when making decisions about use of NIs for either prophylaxis or treatment of influenza. This study is registered as PROSPERO CRD42012002245. The National Institute for Health Research Health Technology Assessment programme.

Prevention of a Nosocomial Infection Caused by Influenza Virus A Using Prophylactic Administration of Oseltamivir: An Observational Study with Review of the Literature

Influenza virus infection in hospitals is a very important clinical issue. The objective of this study was to describe the effect of oseltamivir in controlling a nosocomial influenza virus infection with an observational study and case report. Intervention was carried out in a ward of the University of the Ryukyus Hospital. Symptomatic staff members were sent home for one week, and the infected inpatients were isolated. In addition, in an episode of influenza infection among the staff members and inpatients, oseltamivir (75 mg once a day for 7 days) was administered to all staff members as well as inpatients who had had close contact with the influenza patients. In the hospital ward, eight staff members (nurses and doctors) and ten hospitalized patients were definitively diagnosed with influenza A viral infection based on results of a rapid diagnostic test. Although a relatively large number of the staff members and inpatients had an influenza virus infection, it was possible that the use of oseltamivir efficiently minimized a nosocomial outbreak. It was very difficult to diagnose influenza A virus infection based on clinical symptoms. It was possible to minimize and end the outbreak immediately by using oseltamivir prophylaxis. With a review of the literature, it is considered that prophylaxis with anti‐influenza drugs are highly recommended in hospital settings.

Oseltamivir Prophylaxis Reduces Inflammation and Facilitates Establishment of Cross-Strain Protective T Cell Memory to Influenza Viruses.

CD8+ T cells directed against conserved viral regions elicit broad immunity against distinct influenza viruses, promote rapid virus elimination and enhanced host recovery. The influenza neuraminidase inhibitor, oseltamivir, is prescribed for therapy and prophylaxis, although it remains unclear how the drug impacts disease severity and establishment of effector and memory CD8+ T cell immunity. We dissected the effects of oseltamivir on viral replication, inflammation, acute CD8+ T cell responses and the establishment of immunological CD8+ T cell memory. In mice, ferrets and humans, the effect of osteltamivir on viral titre was relatively modest. However, prophylactic oseltamivir treatment in mice markedly reduced morbidity, innate responses, inflammation and, ultimately, the magnitude of effector CD8+ T cell responses. Importantly, functional memory CD8+ T cells established during the drug-reduced effector phase were capable of mounting robust recall responses. Moreover, influenza-specific memory CD4+ T cells could be also recalled after the secondary challenge, while the antibody levels were unaffected. This provides evidence that long-term memory T cells can be generated during an oseltamivir-interrupted infection. The anti-inflammatory effect of oseltamivir was verified in H1N1-infected patients. Thus, in the case of an unpredicted influenza pandemic, while prophylactic oseltamivir treatment can reduce disease severity, the capacity to generate memory CD8+ T cells specific for the newly emerged virus is uncompromised. This could prove especially important for any new influenza pandemic which often occurs in separate waves.

956Management of a respiratory outbreak due to concomitantly circulating influenza A and parainfluenza 1 in a residential care facility

Introduction: Respiratory viruses are common causes of outbreaks in residential care. Multiplex PCR assays for respiratory viruses enable the detection of multiple viruses, though the clinical significance of dual infections is unclear. We describe an outbreak of 2 respiratory viruses cocirculating in a residential care facility in Vancouver, Canada. Methods: Outbreak investigation was conducted in a facility with 216 residents distributed among 3 separate units in January 2014. Cases were defined as any resident or staff with acute onset respiratory illness [fever (>38.0°C) and cough], and with at least one of the following: sore throat, nasal congestion, malaise, chills, muscle aches, headache or change in mental status. Affected patients were placed on contact and droplet precautions. Nasopharyngeal swabs were collected on symptomatic residents and tested using an in-house multiplex PCR assay (influenza A/B, respiratory syncytial virus, parainfluenza 1/2/3, adenovirus and human metapneumovirus). An epidemic curve of the outbreak was created. Results: The outbreak persisted for 13 days. Twelve patients were infected, including 7 with parainfluenza 1, 2 with influenza A and 3 with parainfluenza 1/influenza A co-infection (Figure 1). All patients manifesting respiratory symptoms were tested (12/28, 43%), rather than empirically treating subsequent patients meeting case definition. Treatment with oseltamivir was provided for 5 patients positive for influenza A, with all others receiving prophylaxis. Two staff developed upper respiratory tract symptoms and were considered cases. Outbreak management also included cessation of group activities, closure to admissions and enhanced unit cleaning. Influenza vaccination rates were 94% for residents and 83% for healthcare workers. Conclusion: Routine testing using a multiplex PCR assay detected a respiratory outbreak involving single and co-infections. Two circulating viruses can affect outbreak management. In this outbreak, all symptomatic residents were tested and confirmed rather than empirically treated. In addition to accurate classification and management of cases, overall consumption of oseltamivir prophylaxis can be reduced by monitoring for the persistence of both viruses.

Oseltamivir prophylaxis in controlling influenza outbreak in nursing homes: a comparison between three different approaches.

To assess influenza outbreaks in nursing homes (NHs) using different pharmacological preventive measures. We compared characteristics of influenza A outbreaks that occurred during 2011/2012 influenza season in three NHs of similar size (208, 167, and 164 residents in NH1, NH2, and NH3, respectively) implementing comparable treatment approaches and non-pharmacological outbreak control measures but different prophylactic pharmacological interventions including oseltamivir 75 mg o.d. for 10 days for all residents (NH1), for directly exposed residents (NH2), and no prophylaxis (NH3). The proportions of residents who developed acute respiratory infection (ARI) in the course of influenza outbreak were 55/208 (26.4 %) in NH1, 64/167 (38.3 %) in NH2, and 31/164 (18.9 %) in NH3; hospital admission was required in 2/55 (3.6 %), 5/64 (7.8 %), and 5/31 (16.1 %) residents of NH1, NH2, and NH3, respectively, while 1/55 (1.8 %), 1/64 (1.6 %), and 3/31 (9.7 %) residents of the corresponding NHs died during influenza outbreak. The duration of the outbreak was shorter in the NH1 where oseltamivir prophylaxis was instituted for all residents (8 days), than in NHs where selective prophylaxis with oseltamivir and no prophylaxis were used (14 and 12 days, respectively). The calculated vaccine effectiveness in residents was 48, 71, and 44 % in NH1, NH2, and NH3, respectively. Staff members had similar ARI attack rate but in comparison to residents were less often vaccinated against influenza and demonstrated higher influenza vaccine effectiveness. Comparison of influenza outbreaks in three NHs revealed that the duration of the outbreak was the shortest in the NH where prophylaxis with oseltamivir was given to all residents.