Emergence and possible transmission of amantadine-resistant viruses during nursing home outbreaks of influenza A (H3N2)

Fighting the flu: a brief review on anti-influenza agents

The influenza virus causes one of the most prevalent and lethal infectious viral diseases of the respiratory system; the disease progression varies from acute self-limiting mild fever to disease chronicity and death. Although both the preventive and treatment measures have been vital in protecting humans against seasonal epidemics or sporadic pandemics, there are several challenges to curb the influenza virus such as limited or poor cross-protection against circulating virus strains, moderate protection in immune-compromised patients, and rapid emergence of resistance. Currently, there are four US-FDA-approved anti-influenza drugs to treat flu infection, viz. Rapivab, Relenza, Tamiflu, and Xofluza. These drugs are classified based on their mode of action against the viral replication cycle with the first three being Neuraminidase inhibitors, and the fourth one targeting the viral polymerase. The emergence of the drug-resistant strains of influenza, however, underscores the need for continuous innovation towards development and discovery of new anti-influenza agents with enhanced antiviral effects, greater safety, and improved tolerability. Here in this review, we highlighted commercially available antiviral agents besides those that are at different stages of development including under clinical trials, with a brief account of their antiviral mechanisms.

Investigation of genetic variation: Neuraminidase gene of influenza A virus H1N1/pdm09, Shiraz, Iran (2015-2016)

Oseltamivir and antiviral agents are frequently used for the prevention and treatment of influenza infection. However, resistance to oseltamivir has been reported globally due to a mutation in the Influenza virus neuraminidase gene. Such resistance will be detected by genotyping and phenotyping studies of viral isolates. The recent study aimed to determine the genetic mutation of neuraminidase gene in influenza A (H1N1) viruses isolated from children referred to Shiraz tertiary hospitals during 1 year (2015-2016) with influenza-like symptoms. A total of 300 patients were registered and throat samples were taken. The throat swabs were used for viral RNA extraction. Detection of influenza A (H1N1) was performed using the one-step real-time polymerase chain reaction (qRT-PCR) method. From positive isolates for H1N1, 51 random samples were evaluated for neuraminidase gene mutation with the nested PCR-sequencing method. Of 300 cases, 102 (34%) isolates were detected as influenza A (H1N1) pdm09. Based on sequencing results, 2 of the 44 sequenced isolates exhibited H275Y substitution, which presented oseltamivir resistance. In comparison with reference strain, the phylogenetic analysis of sequenced isolates was classified in genogroup 6B. While this result is the first report of emerging oseltamivir-resistant in the southwest of Iran, it is highly recommended to perform these evaluations on the different geographical regions in any prevalence area to plan treatment strategies for influenza.

Detection of adamantane-sensitive influenza A(H3N2) viruses in Australia, 2017: a cause for hope?

For over a decade virtually all A(H3N2) influenza viruses have been resistant to the adamantane class of antivirals. However, during the 2017 influenza season in Australia, 15/461 (3.3%) adamantane-sensitive A(H3N2) viruses encoding serine at residue 31 of the M2 protein were detected, more than the total number identified globally during the last 6 years. A return to wide circulation of adamantane-sensitive A(H3N2) viruses would revive the option of using these drugs for treatment and prophylaxis.

Antiviral Resistance in Influenza Viruses: Clinical and Epidemiological Aspects

There are three classes of antiviral drugs approved for the treatment of influenza: the M2 ion channel inhibitors (amantadine, rimantadine), neuraminidase (NA) inhibitors (laninamivir, oseltamivir, peramivir, zanamivir), and the protease inhibitor (favipiravir); some of the agents are only available in selected countries [1, 2]. These agents are effective at treating the signs and symptoms of influenza in patients infected with susceptible viruses. Clinical failure has been demonstrated in patients infected with viruses with primary resistance, i.e., antivirals can be present in the virus initially infecting the patient, or resistance may emerge during the course of therapy [3–5]. NA inhibitors are active against all nine NA subtypes recognized in nature [6], including highly pathogenic avian influenza A/H5N1 and recent low-pathogenic avian influenza A/H7N9 viruses [7]. Since seasonal influenza is usually an acute, self-limited illness in which viral clearance usually occurs rapidly due to innate and adaptive host immune responses, the emergence of drug-resistant variants would be anticipated to have limited effect on clinical recovery in otherwise healthy patients, as has been demonstrated clinically [3, 8, 9]. Unfortunately, immunocompromised or immunologically naïve hosts, such as young children and infants or those exposed to novel strains, are more likely to have mutations that confer resistance emergence during therapy; such resistant variants may also result in clinically significant adverse outcomes [10–13].

In vitro Inhibitory Effects of Combinations of anti-Influenza Agents

To assess the possible interactions among candidate anti-influenza agents, dual combinations of rimantadine, ribavirin, 2′-deoxy-2′-fluoroguanosine (2-FDG) and 4-guanidino-Neu5Ac2en (GG167) were tested against clinical isolates of influenza A H3N2 and H1N1 subtype viruses in MDCK cells by ELISA. Each of the dual combinations showed additive effects, except for the combination of 2-FDG and ribavirin which was synergistic against the influenza A (H1N1) virus. However, this combination also showed enhanced cytotoxicity. In this assay system, influenza agents with differing mechanisms of antiviral interaction interacted in an additive fashion with respect to inhibition of viral replication.

Infection Prevention and Control in the Long-Term-Care Facility

More than 1.5 million residents reside in US nursing homes. In recent years, the acuity of illness of nursing home residents has increased. Long-term-care facility residents have a risk of developing nosocomial infection that is similar to acute-care hospital patients. A great deal of information has been published concerning infections in the long-term-care facility, and infection control programs are nearly universal.

This position paper reviews the literature on infections and infection control programs in the long-term-care facility, covering such topics as tuberculosis, bloodborne pathogens, epidemics, isolation systems, immunization, and antibiotic-resistant bacteria. Recommendations are developed for long-term-care infection control programs based on interpretation of currently available evidence. The recommendations cover the structure and function of the infection control program, including surveillance, isolation, outbreak control, resident care, and employee health. Infection control resources also are presented.

Prevention of Nosocomial Influenza

Objective:

To study compliance with preventive strategies at a university hospital during an outbreak of nosocomial influenza A during the winter of 1988, and the rates of vaccination of healthcare workers and of nosocomial influenza following changes in vaccine practices after the outbreak.

Design:

Retrospective review of employee health, hospital epidemiology, hospital computing, and clinical microbiology records.

Setting:

A university hospital.

Interventions:

Unvaccinated personnel with exposure within the previous 72 hours to an unisolated case of influenza were offered influenza vaccine and 14 days of amantadine hydrochloride prophylaxis. Personnel with exposure more than 72 hours before evaluation were offered vaccine. A mobile cart was introduced for vaccinating personnel after the 1988 outbreak.

Results:

An outbreak of influenza with 10 nosocomial cases occurred in 1988. Only 4% of exposed employees had been vaccinated previously and 23% of exposed, unvaccinated employees agreed to take vaccine, amantadine, or both. A mobile-cart vaccination program was instituted, and annual vaccination rates steadily increased from 26.3% in 1989 to 1990 to 38% in 1993 to 1994 (P<.0001). The relative frequency of documented cases of influenza in employees with symptoms of influenza decreased significantly during this period (P=.025), but nosocomial influenza rates among patients did not change significantly.

Conclusion:

A mobile-cart influenza vaccination program was associated with a significant increase in compliance among healthcare workers, but a majority still remained unvaccinated. The rate of nosocomial influenza among patients was not reduced by the modest increase in the vaccination rate, but influenza rates remained acceptably low, perhaps due to respiratory isolation of patients and furlough of employees with influenza.

A packaged paper fluidic-based microdevice for detecting gene expression of influenza A virus

Pathotyping and subtyping of influenza A virus were performed with a packaged paper fluidic-based analytical microdevice (PFAM) after one-step reverse transcription-polymerase chain reaction (RT-PCR). The PFAM contains two test lines: one for detecting M gene to identify the influenza A virus and another for haemagglutinin subtyping to determine the viral strain among H1N1, H3N2, and H5N1. The M gene and the haemagglutinin gene (H1, H3, and H5 genes) were amplified by using the Digoxigenin and the Texas Red modified primers, respectively, in the multiplex RT-PCR. The amplicon products were loaded in the conjugate pad of the PFAM in which the streptavidin coated gold nanoparticles were linked with the biotin moieties that were incorporated in the middle of the DNA strands, and then captured by the anti-Digoxigenin and anti-Texas Red immobilized on the test lines. Influenza A H1N1, H3N2, and H5N1 could be identified with a limit of detection of 10(2) copies of RNA templates in 10 min. Pathotyping and subtyping of the clinical nasopharyngeal swab samples were also analyzed whose results were confirmed by real-time RT-PCR.

Influenza outbreak control practices and the effectiveness of interventions in long-term care facilities: a systematic review

Background

Evaluation of influenza control measures frequently focuses on the efficacy of chemoprophylaxis and vaccination, while the effectiveness of non-pharmaceutical interventions (NPI) receives less emphasis. While influenza control measures are frequently reported for individual outbreaks, there have been few efforts to characterize the real-world effectiveness of these interventions across outbreaks.

Objectives

To characterize influenza case and outbreak definitions and control measures reported by long-term care facilities (LTCFs) of elderly adults and estimate the reduction in influenza-like illness (ILI) attack rates due to chemoprophylaxis and NPI.

Methods

We conducted a literature search in PubMed including English-language studies reporting influenza outbreaks among elderly individuals in LTCFs. A Bayesian hierarchical logistic regression model estimated the effects of control measures on ILI attack rates.

Results

Of 654 articles identified in the literature review, 37 articles describing 60 influenza outbreaks met the inclusion criteria. Individuals in facilities where chemoprophylaxis was used were significantly less likely to develop influenza A or B than those in facilities with no interventions [odds ratio (OR) 0·48, 95% CI: 0·28, 0·84]. Considered by drug class, adamantanes significantly reduced infection risk (OR 0·22, 95% CI: 0·12, 0·42), while neuraminidase inhibitors did not show a significant effect. Although NPI showed no significant effect, the results suggest that personal protective equipment may produce modest protective effects.

Conclusions

Our results indicate pharmaceutical control measures have the clearest reported protective effect in LTCFs. Non-pharmaceutical approaches may be useful; however, most data were from observational studies and standardized reporting or well-conducted clinical trials of NPI are needed to more precisely measure these effects.

Ching-fang-pai-tu-san inhibits the release of influenza virus

ETHNOPHARMACOLOGICAL RELEVANCE

Ching-fang-pai-tu-san (CFPTS) is a Chinese herbal decoction that is used as a cure for the common cold, fever, headache, and poor circulation. However, no previous studies have investigated the mode of action of CFPTS against influenza virus infections. To investigate the antiviral mechanism of CFPTS, we examined viral entry, transcription, translation, viral glycoprotein hemagglutinin (HA) transport, and budding of the influenza virus.

MATERIALS AND METHODS

The antiviral activity of nontoxic concentrations of CFPTS against influenza virus A/WSN/33 was examined by assaying (neutralization assay) its inhibition of the virus-induced cytopathic effects. The mode of CFPTS action was first examined with a time-of-addition assay of synchronized infections, followed by monitoring HA transport by immunofluorescence microscopy. Viral endocytosis was evaluated with attachment and penetration assays. The inhibition of viral replication was measured by quantitative real-time PCR, immunoblotting, and immunofluorescence microscopy. We also performed assays related to the inhibition of viral entry, such as neuraminidase activity and hemagglutinin activity assays.

RESULTS

Based on the inhibition of the virus-induced cytopathic effect in Madin-Darby canine kidney cells, the EC(50) of CFPTS was about 1.44 ± 0.22 mg/mL against influenza virus A/WSN/33. CFPTS displayed a broad spectrum of inhibitory activities against different strains of influenza A virus, as well as some enteroviruses. However, this extract proved less effective against clinical oseltamivir-resistant strains and influenza B viruses. CFPTS did not suppress viral RNA or protein synthesis. According to a time-of-addition assay, the antiviral mechanism of CFPTS may involve viral budding or intracellular viral glycoprotein transport. A plaque reduction assay showed that CFPTS reduced both the plaque size and plaque quantity. The intracellular transport of viral glycoprotein hemagglutinin was blocked by CFPTS by immunofluorescence microscopic analysis. Thus, it is possible that the antiviral mechanism of CFPTS might inhibit the assembly of progeny virions and/or their subsequent release.

CONCLUSIONS

Our results give scientific support to the use of CFPTS in the treatment of influenza virus infections. CFPTS has potential utility in the management of seasonal pandemics of influenza virus infections, like other clinically available drugs.

Viral infections of the respiratory tract: prevention and treatment

The rapid discovery of specific viral agents as the cause of many acute respiratory diseases was accompanied by considerable optimism that vaccines or other control measures could be developed quickly. Subsequent experience has demonstrated that effective control of these important public health problems has been an elusive goal. However, recent exciting developments in our understanding of the molecular biology and immunology of these viruses may provide the basis for more effective strategies in the future.

Antiviral Resistance in Influenza Viruses: Clinical and Epidemiological Aspects

Two classes of anti-viral agents, the M2 ion channel inhibitors (amantadine, rimantadine) and neuraminidase (NA) inhibitors (oseltamivir, zanamivir) are available for treatment and prevention of infl uenza in most countries of the world. The principle concerns about emergence of antiviral resistance in infl uenza viruses are loss of drug effi cacy, transmission of resistant variants, and possible increased virulence or transmissibility of resistant variants (1). Because seasonal infl uenza is usually an acute, self-limited illness in which viral clearance occurs rapidly due to innate and adaptive host immune responses, the emergence of drug-resistant variants would be anticipated to have modest effects on clinical recovery, except perhaps in immunocompromised or immunologically naïve hosts, such as young infants or during the appearance of a novel strain. In contrast to the limited impact of resistance emergence in the treated immunocompetent individual, the epidemiologic impact of resistance emergence and transmission could be considerable, including loss of both prophylactic and therapeutic activity for a particular drug, at the household, community, or perhaps global level. Infl uenza epidemiology in temperate climates is expected to provide some protection against widespread circulation of resistant variants, as viruses do not persist between epidemics but rather are re-introduced each season and new variants appear often (2, 3).

Antivirals and influenza: frequency of resistance

Antivirals are effective in prophylaxis and therapy for influenza and are likely to be active against a new pandemic variant. They can be divided into the M2 inhibitors, adamantane and rimantadine, and the neuraminidase inhibitors (NAIs), zanamivir and oseltamivir. The former are limited in activity to type A viruses, whereas the latter are also active against type B viruses. Both classes of drugs appear similarly efficacious in prophylaxis at approximately 70-90%. However, use of M2 inhibitors (adamantanes) in therapy is limited by side effects, more common with amantadine, and also by production of antiviral resistance and lack of demonstrated prevention of complications. The NAIs prevent both types of seasonal influenza, shorten duration of illness, and reduce complications. As such, their use for seasonal influenza treatment has been increasing. They are active against A(H5N1) but oseltamivir has been most extensively stockpiled because the infection in humans may be disseminated. Resistance does emerge, but not at the same frequency as with the M2 inhibitors. Resistant viruses also appear less fit and thus less able to spread. However, as use increases, resistance needs to be carefully monitored.

Control of an outbreak due to an adamantane-resistant strain of influenza A (H3N2) in a chronic care facility

BACKGROUND

Chronic care facility residents are at risk of severe influenza infection and death. Adamantanes have been used by chronic care facilities for influenza A prophylaxis; however, genotypic resistance has altered prophylaxis recommendations. An outbreak of influenza A (H3N2) in a chronic care facility housing neurologically impaired children and young adults and subsequent control measures are described.

PATIENTS AND METHODS

Resident charts were retrospectively reviewed. Isolates were characterized by strain identification and pyrosequencing.

RESULTS

Although 95 (97%) of 98 residents had been immunized against influenza at the start of the influenza season, 16 (84%) of 19 case patients were identified on the first floor. However, following implementation of enhanced infection control practices and adamantane prophylaxis, only 10 (13%) of 79 case patients were identified on the second floor. Subsequent pyrosequencing studies revealed a serine to asparagine mutation at position 31 of the M2 protein.

CONCLUSIONS

Enhanced infection control precautions and adamantane prophylaxis were used to control spread of influenza in a chronic care facility. This outbreak demonstrates the importance of timely and consistent implementation of infection control measures in controlling influenza outbreaks in long term care facilities and raises questions about a possible role for adamantanes in preventing transmission of adamantane-resistant influenza A viruses.

Antiviral Drugs for the Control of Pandemic Influenza Virus

In the advent of an influenza virus pandemic it is likely that the administration of antiviral drugs will be an important first line of defence against the virus. The drugs currently in use are effective against seasonal influenza virus infection, and some cases have been used in the treatment of patients infected with the avian H5N1 influenza virus. However, it is becoming clear that the emergence of drug-resistant viruses will potentially be a major problem in the future efforts to control influenza virus infection. In addition, during a new pandemic, sufficient quantities of these agents will need to be distributed to many different parts of the world, possibly at short notice. In this review we provide an overview of some of the drugs that are currently available for the treatment and prevention of influenza virus infection. In addition, basic research on influenza virus is providing a much better understanding of the biology of the virus, which is offering the possibility of new anti-influenza virus drugs. We therefore also review some new antiviral strategies that are being reported in the scientific literature, which may form the basis of the next generation of antiviral strategies during a future influenza virus pandemic. Key words: Antiviral, Amantadine, Pandemic influenza virus, Oseltamivir, siRNA

Adamantane-resistant influenza infection during the 2004-05 season

Adamantane-resistant influenza A is an emerging problem, but infections caused by resistant and susceptible viruses have not been compared. We identified adamantane resistance in 47% of 152 influenza A virus (H3N2) isolates collected during 2005. Resistant and susceptible viruses caused similar symptoms and illness duration. The prevalence of resistance was highest in children.

Inhaled zanamivir versus rimantadine for the control of influenza in a highly vaccinated long-term care population

BACKGROUND

Despite vaccination, influenza commonly causes morbidity and mortality in institutional settings. Influenza control with rimantadine and amantadine is limited by emergence and transmission of drug-resistant influenza A variants, ineffectiveness against influenza B, and toxicity. This study evaluated the efficacy and tolerability of zanamivir versus rimantadine for influenza outbreak control in long-term care facilities.

METHODS

This double-blind, randomized, controlled study prospectively enrolled nursing home residents for 3 influenza seasons (1997 to 2000). Vaccine was offered to all subjects. Following influenza outbreak declaration, subjects were randomized to inhaled zanamivir 10 mg or standard of care (rimantadine 100 mg for influenza A or placebo for influenza B) once daily for 14 days. The proportion of randomized subjects developing symptomatic, laboratory-confirmed influenza during prophylaxis was the primary endpoint.

RESULTS

Of 482 randomizations (238 zanamivir, 231 rimantadine, 13 placebo), 96% of subjects were elderly or had high-risk conditions; over 90% were vaccinated. Symptomatic, laboratory-confirmed influenza occurred in 3% of zanamivir subjects and 8% of rimantadine subjects during chemoprophylaxis (P = .038; additional protective efficacy for zanamivir over rimantadine = 61%). Since only 25 subjects were randomized during 2 influenza B outbreaks and none developed influenza, the influenza B data were excluded from further analysis. Zanamivir was well tolerated and unassociated with emergence of resistant virus; rimantadine-resistant variants were common.

CONCLUSIONS

This is the first prospective, controlled study demonstrating effectiveness of chemoprophylaxis for influenza outbreak control. Zanamivir prevents symptomatic, laboratory-confirmed influenza more effectively than rimantadine, is unassociated with resistant virus, and has a favorable safety profile. Zanamivir is an appropriate alternative for influenza outbreak control among institutionalized vaccinated elderly.

Meningococcal, influenza virus, and hepatitis B virus vaccination coverage level among health care workers in Hajj

Background

The objective of this study was to assess the compliance of health care workers (HCWs) employed in Hajj in receiving the meningococcal, influenza, and hepatitis B vaccines.

Methods

A cross-sectional survey of doctors and nurses working in all Mena and Arafat hospitals and primary health care centers who attended Hajj-medicine training programs immediately before the beginning of Hajj of the lunar Islamic year 1423 (2003) using self-administered structured questionnaire which included demographic data and data on vaccination history.

Results

A total of 392 HCWs were studied including 215 (54.8%) nurses and 177 (45.2%) doctors. One hundred and sixty four (41.8%) HCWs were from Makkah and the rest were recruited from other regions in Saudi Arabia. Three hundred and twenty three (82.4%) HCWs received the quadrivalent (ACYW135) meningococcal meningitis vaccine with 271 (83.9%) HCWs receiving it at least 2 weeks before coming to Hajj, whereas the remaining 52 (16.1%) HCWs received it within < 2 weeks. Only 23 (5.9%) HCWs received the current year's influenza virus vaccine. Two hundred and sixty (66.3%) of HCWs received the three-dose hepatitis B vaccine series, 19.3% received one or two doses, and 14.3% did not receive any dose. There was no statistically significant difference in compliance with the three vaccines between doctors and nurses.

Conclusion

The meningococcal and hepatitis B vaccination coverage level among HCWs in Hajj was suboptimal and the influenza vaccination level was notably low. Strategies to improve vaccination coverage among HCWs should be adopted by all health care facilities in Saudi Arabia.

The use of antiviral drugs for influenza: recommended guidelines for practitioners

The present document outlines current guidelines and supporting literature relating to the use of antiviral drugs for chemoprophylaxis and influenza illness therapy in paediatric and adult settings. The focus is on the management of influenza in interpandemic periods. Where appropriate, the areas in need of additional research are identified. It will be necessary to update aspects of these guidelines as new information emerges. The recommendations that follow represent the results of a joint effort supported by the Canadian Paediatric Society and the Association of Medical Microbiology and Infectious Disease Canada.

Detection of influenza viruses resistant to neuraminidase inhibitors in global surveillance during the first 3 years of their use

Emergence of influenza viruses with reduced susceptibility to neuraminidase inhibitors (NAIs) develops at a low level following drug treatment, and person-to-person transmission of resistant virus has not been recognized to date. The Neuraminidase Inhibitor Susceptibility Network (NISN) was established to follow susceptibility of isolates and occurrence of NAI resistance at a population level in various parts of the world. Isolates from the WHO influenza collaborating centers were screened for susceptibilities to oseltamivir and zanamivir by a chemiluminescent enzyme inhibition assay, and those considered potentially resistant were analyzed by sequence analysis of the neuraminidase genes. During the first 3 years of NAI use (1999 to 2002), 2,287 isolates were tested. Among them, eight (0.33%) viruses had a >10-fold decrease in susceptibility to oseltamivir, one (0.22%) in 1999 to 2000, three (0.36%) in 2000 to 2001, and four (0.41%) in 2001 to 2002. Six had unique changes in the neuraminidase gene compared to neuraminidases of the same subtype in the influenza sequence database. Although only one of the mutations had previously been recognized in persons receiving NAIs, none were from patients who were known to have received the drugs. During the 3 years preceding NAI use, no resistant variants were detected among 1,054 viruses. Drug use was relatively stable during the period, except for an approximate 10-fold increase in oseltamivir use in Japan during the third year. The frequency of variants with decreased sensitivity to the NAIs did not increase significantly during this period, but continued surveillance is required, especially in regions with higher NAI use.

Antivirals for influenza: historical perspectives and lessons learned

The development of the currently available classes of antivirals, the M2 proton channel inhibitors and the neuraminidase inhibitors, provides valuable perspectives relevant to the field of antiviral chemotherapy in general and insights into aspects of viral pathogenesis and antiviral resistance relevant specifically to influenza. The efficacy observed with these antiviral drugs has proven the importance of these antiviral targets, as well as the principle that chemoprophylaxis and early treatment are possible in influenza infections with small molecular weight inhibitors.

Inhaled Zanamivir Versus Placebo for the Prevention of Influenza Outbreaks in an Unvaccinated Long-term Care Population

BACKGROUND

Antiviral chemoprophylaxis effectiveness for influenza control has not been prospectively established for unvaccinated residents of long-term care facilities. This study evaluated the efficacy and tolerability of zanamivir against the standard of care (no intervention, ie, placebo) for influenza outbreak control in a largely unvaccinated institutionalized population.

OBJECTIVE

To evaluate the efficacy and tolerability of zanamivir versus placebo for influenza outbreak control in long-term care facilities.

METHODS

This double-blind, randomized, placebo-controlled study prospectively enrolled/followed residents of long-term care facilities (LTCF) at 12 centers for 1 to 3 influenza seasons (1997 to 2000). Following influenza outbreak declaration, asymptomatic subjects were randomized for prophylaxis to inhaled zanamivir 10 mg or inhaled placebo given once daily for 14 days. The proportion of randomized subjects who during prophylaxis developed symptomatic, laboratory-confirmed influenza (SLCI) was the primary end point.

RESULTS

Influenza outbreaks were explosive. The attack rates varied from 9.5 to 14.8 per 100 residents. Of 1763 consents given and resulting in 494 randomizations, 49% received zanamivir and 51% placebo; 66% were elderly and 9% were vaccinated. SLCI occurred in 6% of zanamivir and 9% of placebo subjects (P = .355; protective efficacy for zanamivir = 29%, 95% confidence interval 31% to 62%), and symptomatic influenza confirmed by culture in 2% and 6%, respectively (P = .052; protective efficacy = 65%, 95% confidence interval 8.5% to 86%). Zanamivir use was also associated with a 70% (95% confidence interval 13% to 89%) reduction in laboratory-confirmed influenza with fever (2% vs 6%, P = .043). Influenza B was not detected. Zanamivir was well tolerated. No virus isolate demonstrated zanamivir resistance.

CONCLUSIONS

The protective efficacy of zanamivir versus placebo for SLCI was marginal, for all laboratory confirmed illnesses, but significant against culture proven and febrile influenza, suggesting zanamivir can be effective for outbreak control and symptom reduction of unvaccinated institutionalized residents. Zanamivir had an acceptable safety profile in elderly, high-risk LTCF residents and was not associated with the emergence of resistant strains.

Incidence of adamantane resistance among influenza A (H3N2) viruses isolated worldwide from 1994 to 2005: a cause for concern

BACKGROUND

Adamantanes have been used to treat influenza A virus infections for many years. Studies have shown a low incidence of resistance to these drugs among circulating influenza viruses; however, their use is rising worldwide and drug resistance has been reported among influenza A (H5N1) viruses isolated from poultry and human beings in Asia. We sought to assess adamantane resistance among influenza A viruses isolated during the past decade from countries participating in WHO's global influenza surveillance network.

METHODS

We analysed data for influenza field isolates that were obtained worldwide and submitted to the WHO Collaborating Center for Influenza at the US Centers for Disease Control and Prevention between Oct 1, 1994, and Mar 31, 2005. We used pyrosequencing, confirmatory sequence analysis, and phenotypic testing to detect drug resistance among circulating influenza A H3N2 (n=6524), H1N1 (n=589), and H1N2 (n=83) viruses.

FINDINGS

More than 7000 influenza A field isolates were screened for specific aminoacid substitutions in the M2 gene known to confer drug resistance. During the decade of surveillance a significant increase in drug resistance was noted, from 0.4% in 1994-1995 to 12.3% in 2003-2004. This increase in the proportion of resistant viruses was weighted heavily by those obtained from Asia with 61% of resistant viruses isolated since 2003 being from people in Asia.

INTERPRETATION

Our data raise concerns about the appropriate use of adamantanes and draw attention to the importance of tracking the emergence and spread of drug-resistant influenza A viruses.

Economic evaluation of oseltamivir phosphate for postexposure prophylaxis of influenza in long-term care facilities

OBJECTIVES

To compare the cost-effectiveness of oseltamivir postexposure prophylaxis during influenza A outbreaks with that of amantadine postexposure prophylaxis or no postexposure prophylaxis in long-term care facilities (LTCFs).

DESIGN

Cost-effectiveness analysis based on decision analytic model from a government-payer perspective.

SETTING

A Canadian LTCF, with high staff vaccination, at the beginning of influenza season.

PARTICIPANTS

Elderly, influenza-vaccinated patients living in a Canadian LTCF.

MEASUREMENTS

Incremental costs (or savings) per influenza-like illness case avoided compared with usual care.

RESULTS

From a government-payer perspective, this analysis showed that oseltamivir was a dominant strategy because it was associated with the fewest influenza-like illness cases, with cost savings of $1,249 per 100 patients in 2001 Canadian dollars compared with amantadine and $3,357 per 100 patients compared with no prophylaxis. Costs for amantadine dose calculation and hospitalization for adverse events contributed to amantadine being a more-expensive prophylaxis strategy than oseltamivir. Both prophylaxis strategies were more cost-effective than no prophylaxis.

CONCLUSION

Despite high influenza vaccination rates, influenza outbreaks continue to emerge in LTCFs, necessitating cost-effective measures to further limit the spread of influenza and related complications. Although amantadine has a lower acquisition cost than oseltamivir, it is associated with more adverse events, lower efficacy, and individualized dosing requirements, leading to higher overall costs and more influenza-like illness cases than oseltamivir. Therefore the use of oseltamivir postexposure prophylaxis is more cost-effective than the current standard of care with amantadine prophylaxis or no prophylaxis.

Development of antivirals against influenza

Morbidity and mortality due to influenza virus infections remain a major problem throughout the world. Yearly, medical costs and loss of productivity resulting from influenza infection are estimated to be in the range of 12 dollars bn in the USA. The predicted increases in the elderly and immune-deficient populations will make influenza an even greater threat in the future. Despite the availability of vaccines, they have been least effective in these high-risk populations. Coupled with the requirement for routine revaccination, the need for effective antiviral agents is illustrated. The currently approved drugs, amantadine, rimantadine and ribavirin (in some countries), have limitations. They are only inhibitory against influenza A viruses, are prone to adverse reactions and quickly give rise to resistant virus. This review examines current drug therapies, antivirals in development and possible future opportunities for anti-influenza drugs.

Antiviral therapy for influenza : a clinical and economic comparative review

Each year influenza epidemics cause a considerable burden of disease. Vaccination against influenza A and B viruses has been and remains the cornerstone of influenza prevention, but antiviral therapy can serve as an important adjunct to vaccination in controlling the impact of the disease. Two classes of drugs are currently licensed in a large number of countries for the treatment of influenza. The M2 ion channel blockers or amantadanes (amantadine and rimantadine) are specific inhibitors of influenza A virus replication, whereas the neuraminidase inhibitors (zanamivir and oseltamivir) are active against influenza A and B viruses. Readily transmissible drug-resistant viruses develop frequently during amantadane treatment but not during neuraminidase inhibitor treatment. In this review, efficacy and safety data from randomised controlled trials are evaluated to gain an understanding of what we can and cannot expect from antiviral treatment. All four drugs shorten the course of influenza disease by approximately 1 day and relieve symptoms to some extent, but there is still uncertainty as to whether antiviral therapy leads to a reduction of serious complications and hospitalisation. The results of cost-effectiveness analyses are very diverse, in part because of differences in methodology but also because there is no consensus on what probabilities to assign to the key risks and benefits that form the basis of these studies. Consensus statements by advisory bodies in England and Germany recommend neuraminidase inhibitors for the therapy of influenza in high-risk individuals such as people over 65 years or under 2 years, and individuals with chronic cardiovascular, pulmonary or renal disease, diabetes mellitus or immunosuppression. However, there is no agreement as to whether antiviral therapy can be generally recommended for otherwise healthy children and adults. The availability of safe and effective antiviral therapy options should be kept in mind by the practising clinician, while more specific recommendations and policy formulation will depend on additional efficacy data that include frequency of complications and hospitalisation as outcome measures.

Antiviral treatment and prophylaxis of influenza in primary care: German recommendations

Antiviral drugs are a valuable supplementation to vaccines for the control and prevention of influenza. In Germany, for treating influenza amantadine, oseltamivir and zanamivir are approved. Amantadine and oseltamivir are also licensed for prophylactic use. On behalf of the Paul-Ehrlich-Society of Germany and the German Association for the Control of Virus Diseases, as two independent scientific societies, the first consensus Conference on the Antiviral Treatment and Prophylaxis of Influenza was held in June 2002. Based on the available data of clinical studies an expert group developed the following recommendations for the appropriate clinical use of the antiviral drugs: (1) since oseltamivir (orally administered) and zanamivir (administered by inhalation) have apparently similar clinical efficacy both drugs can be used alternatively for treatment. (2) Amantadine is not an alternative to the neuraminidase (NA) inhibitors because it is not effective against influenza B viruses, it frequently selects resistant virus mutants and it can cause adverse events. (3) When influenza is prevalent in the community patients with the clinical diagnosis of influenza should be treated with neuraminidase inhibitors if the symptoms are lasting not longer than 48 h. (4) Immunocompetent patients with a non-febrile illness and patients with a symptom history of more than 2 days should not be treated with antiviral drugs. (5) Although there are no data from clinical trials immunocompromised patients should also be treated when influenza has been diagnosed. (6) The prophylactic use of antiviral drugs can be recommended for persons with close contact to acutely ill persons and no recent vaccination against influenza. (7) The use of anti-influenza drugs have to be considered for prophylaxis in pandemics. A precondition for the adequate use of anti-influenza drugs in the primary medical care is the timely information on the local influenza situation delivered by surveillance systems.

Emergence of amantadine-resistant influenza A viruses: epidemiological study

At present, three licensed antiviral influenza agents are available in Japan: amantadine, zanamivir, and oseltamivir. These antiviral agents can be used for controlling and preventing influenza, but they are not a substitute for vaccination. Amantadine is an antiviral drug with activity against influenza A viruses, but not influenza B viruses. Persons who have influenza A infection and who are treated with amantadine can shed sensitive viruses early in the course of treatment and later shed drug-resistant viruses, especially after 5-7 days of therapy. Such persons can benefit from therapy even when resistant viruses emerge. In screening for amantadine susceptibility, enzyme-linked immunoassays, plaque reduction assays, and TCID50/0.2 ml titration are employed. The molecular changes associated with resistance have been identified as single-nucleotide changes, leading to corresponding amino acid substitutions in one of four critical sites, amino acids 26, 27, 30, and 31, in the transmembrane region of the M2 protein. The polymerase chain reaction (PCR)-restriction fragment length polymorphism analysis method is quite useful. Resistant viruses have been circulated in outbreak situations at nursing homes where amantadine was used not only for treating influenza virus infection but also for Parkinson's disease. Measures should be taken to reduce contact, as much as possible, between persons taking and those not taking antiviral drugs for treatment or chemoprophylaxis.

Frequency of amantadine-resistant influenza A viruses during two seasons featuring cocirculation of H1N1 and H3N2

In two influenza seasons during which H1N1 and H3N2 cocirculated, resistance was more frequent in H3N2 strains than in H1N1 strains after amantadine treatment. Predominant amino acid substitutions in M2 protein occurred at position 31 (serine to asparagine) in H3N2 strains and at position 27 (valine to alanine) in H1N1 strains.

Current strategies for management of influenza in the elderly population

Influenza virus remains among the most important pathogens infecting elderly people. Vaccination is the most cost-effective strategy to reduce morbidity and mortality due to influenza. For persons who are not vaccinated or for whom vaccines fail to prevent influenza, there are 2 classes of efficacious drugs for treatment or chemoprophylaxis: M2 channel inhibitors and neuraminidase inhibitors. Effective treatment, however, must commence within 48 h of the onset of symptoms, which can create problems for patients who wait to see whether their symptoms worsen or improve. Older adults who have relocated to the congregate housing environments of assisted living and long-term care facilities deserve special consideration, because influenza exposure risks are different for this group. Strategies for control of influenza must combine preventive approaches, such as vaccination, educational approaches, and the introduction of policies that allow health care professionals anticipate, identify, and efficiently respond to influenza outbreaks.

Use of oseltamivir during influenza outbreaks in Ontario nursing homes, 1999-2000

OBJECTIVES

To describe the experience of Ontario long-term care facilities that used oseltamivir during influenza outbreaks in 1999/2000.

DESIGN

Case series.

SETTING

Ten Ontario long-term care facilities for older people and their residents.

PARTICIPANTS

Older residents of long-term care facilities.

INTERVENTION

Oseltamivir for treatment or prophylaxis during 11 influenza outbreaks in 1999/2000.

MEASUREMENTS

Control of outbreaks; pneumonia, hospitalization, and death complicating acute influenza.

RESULTS

All outbreaks were due to influenza A//H3N2/Sydney/05/97. One facility elected to use oseltamivir for treatment and amantadine for prophylaxis. The remaining nine facilities (10 outbreaks) recommended oseltamivir for treatment and prophylaxis (after amantadine failure in five and as primary prophylaxis in five). Use of oseltamivir was associated with termination of the outbreak in all eight evaluable outbreaks. Overall, 178/185 (96%) case-residents met the case definition of influenza and had complete data for evaluation. Of these, 63 (35%) were treated with antibiotics, 37 (21%) were diagnosed with pneumonia, 19 (11%) were hospitalized, and 16 (9%) died. Compared with residents receiving no therapy or who became ill while taking amantadine, residents who received oseltamivir within 48 hours of the onset of symptoms were less likely to be prescribed antibiotics, to be hospitalized, or to die (P <.05 for each outcome). These differences persisted and remained statistically significant when corrected for influenza immunization status. A total of 730 residents received oseltamivir prophylaxis for a median of 9 days (range 5-12). Of these, side effects were identified in 30 (4.1%), the most common being diarrhea (12 residents, 1.6%), cough (5, 0.7%), confusion (4, 0.5%) and nausea (4, 0.5%).

CONCLUSIONS

Oseltamivir is safe and appears to be effective when used as treatment or prophylaxis to control outbreaks of influenza in older nursing home residents.

Antiviral therapy of influenza

The prevention of influenza virus infections by the use of vaccines remains the most cost-effective and practical method of influenza virus control, but the use of antiviral prophylaxis and treatment in certain populations or high-risk individuals is also possible. Four antiviral drugs are currently licensed in the United States for the treatment and/or prevention of influenza virus infection in children. The M2 blockers, (amantadine and rimantadine) have been licensed for the prophylaxis and treatment of influenza in diverse high-risk populations, including children, for years. Advantages of these agents include the low cost, high oral bioavailability, and relative tolerability of one of these agents (rimantadine) in children. Disadvantages include efficacy against influenza A viruses only (not type B), the relative rapid development of resistance, and adverse effects associated with amantadine in particular (especially in the elderly and those with decreased renal function). Two agents in a new antiviral class, the neuraminidase inhibitors, have been licensed recently for the treatment and prophylaxis of influenza in the United States. Oseltamivir is licensed for the treatment of influenza in children older than 1 year and for the prophylaxis in children older than 13 years. This drug is safe and well-tolerated, and is available in capsules or a liquid suspension. Another neuraminidase inhibitor, zanamivir, is administered as an inhaled powder via a special inhaler device and is licensed for the treatment of influenza in children older than 7 years. Both neuraminidase inhibitors appear to be similarly effective and are not associated with the development of antiviral resistance. No direct comparisons of any of these antiviral agents has been performed; all result in clinical improvement approximately 1 to 2 days earlier in otherwise healthy children when therapy is initiated within 48 hours of onset of symptoms.

Prolonged excretion of amantadine-resistant influenza a virus quasi species after cessation of antiviral therapy in an immunocompromised patient

Phenotypic and molecular studies were conducted to characterize multiple influenza A isolates recovered from an immunocompromised patient who died of viral and fungal pneumonitis. The recovery of amantadine-resistant isolates was correlated with the detection of 2 drug-resistant M2 variants (codons 27 and 31) in combination with a wild-type virus. The mutant viruses persisted within the viral population in variable proportions >1 month after cessation of antiviral therapy. These results confirm animal studies reported elsewhere regarding the genetic stability of influenza M2 mutants and their potential for transmission in humans.

Influenza in the acute hospital setting

Influenza poses special hazards inside healthcare facilities and can cause explosive outbreaks of illness. Healthcare workers are at risk of acquiring influenza and thus serve as an important reservoir for patients under their care. Annual influenza immunisation of high-risk persons and their contacts, including healthcare workers, is the primary means of preventing nosocomial influenza. Despite influenza vaccine effectiveness, it is substantially underused by healthcare providers. Influenza can be diagnosed by culturing the virus from respiratory secretions and by rapid antigen detection kits; recognition of a nosocomial outbreak is important in order to employ infection-control efforts. Optimal control of influenza in the acute-care setting should focus upon reducing potential influenza reservoirs in the hospital, including: isolating patients with suspected or documented influenza, sending home healthcare providers or staff who exhibit typical symptoms of influenza, and discouraging persons with febrile respiratory illness from visiting the hospital during a known influenza outbreak in the community. (Note: influenza and other respiratory viruses can cause non-febrile illness but are still transmissible.) The antiviral M2 protein inhibitors (amantadine, rimantadine) and neuraminidase inhibitors (zanamivir, oseltamivir) have proven efficacy in treating and preventing influenza illness; however, their role in the prevention and control of influenza in the acute hospital setting remains to be more fully studied.

Respiratory Viruses

Acute respiratory disease, including the common cold, influenza-like illness, croup, bronchiolitis, and viral pneumonia, can be caused by a wide variety of viral and non-viral agents. Among the viruses, those with RNA genomes tend to play a more prominent role, particularly among immunologically intact individuals. DNA viruses are also associated with respiratory disease. The characteristics of the viruses most often associated with respiratory disease are described briefly in the chapter. Three distinct types of influenza viruses are recognized, influenza A virus, influenza B virus, and influenza C virus, based on antigenic differences in the nucleoprotein and matrix proteins. All three viruses share certain characteristics, including the presence of a viral envelope containing glycoproteins important for viral entry and egress from cells, and a segmented genome. The standard nomenclature for influenza viruses includes the influenza type, place of initial isolation, strain designation, and year of isolation.

Detection of amantadine-resistant influenza A virus strains in nursing homes by PCR-restriction fragment length polymorphism analysis with nasopharyngeal swabs

Annual consumption of amantadine increased abruptly after its approval for the treatment of influenza A virus infections in Japan in 1998, and the emergence of amantadine-resistant viruses is now a matter of concern. To detect resistant influenza A virus strains, we have developed a PCR-restriction fragment length polymorphism (PCR-RFLP) analysis for nasopharyngeal swabs. Three different primer sets for nested PCR were designed to incorporate restriction sites into the amplicon to differentiate single-amino-acid substitutions at positions 27, 30, and 31 that confer resistance in the transmembrane domain of the M2 protein. Each PCR product was digested with respective endonucleases (BspLU11I for amino acid change at position 27, HhaI for position 30, and ScaI for position 31), and the polymorphisms were determined by electrophoresis. Thirty-four (24.1%) of 141 PCR-positive samples had resistance patterns in eight nursing homes in the 1998-1999 season. Thirty-one viruses (91.2%) showed a change at position 31 (serine to asparagine), three viruses (8.8%) showed a change at position 30 (alanine to threonine), and none showed a change at position 27. The incidence of resistant viruses did not show any significant difference between four facilities where amantadine was used mainly for influenza treatment and four other facilities where it was used only for Parkinson's disease, values being 27.6 and 16.3%, respectively. We have confirmed that the PCR-RFLP method is useful for detecting amantadine-resistant strains directly from nasopharyngeal swabs and that resistant viruses were circulating in nursing homes where the drug was used not only for influenza virus but also for Parkinson's disease.

Long-term use of oseltamivir for the prophylaxis of influenza in a vaccinated frail older population

OBJECTIVES

To investigate the efficacy of once-daily oral oseltamivir for 6 weeks (Tamiflu) in prophylaxis against laboratory-confirmed clinical influenza in frail older subjects living in homes for seniors and to determine the safety and tolerability of long-term oseltamivir.

DESIGN

Double-blind, placebo-controlled, parallel-group, randomized, multicenter study.

SETTING

Thirty-one residential homes for seniors across United States and Europe.

PARTICIPANTS

Five hundred forty-eight frail older occupants (mean age 81 years, >80% vaccinated).

INTERVENTION

Prophylaxis with oseltamivir 75 mg or placebo once daily for 6 weeks, beginning when influenza was detected locally.

MEASUREMENTS

The primary efficacy endpoint was laboratory-confirmed clinical influenza.

RESULTS

Oseltamivir administration resulted in a 92% reduction in the incidence of laboratory-confirmed clinical influenza compared with placebo (placebo 12/272 (4.4%), oseltamivir 1/276 (0.4%); P = .002). Of subjects vaccinated against influenza, oseltamivir was 91% effective in preventing laboratory-confirmed clinical influenza (placebo 11/218 (5.0%), oseltamivir 1/222 (0.5%); P = .003). Oseltamivir use was associated with a significant reduction in the incidence of secondary complications (placebo 7/272 (2.6%), oseltamivir 1/276 (0.4%); P = .037). Although nearly all subjects were taking concomitant medication both before and during the study, oseltamivir was well tolerated. A similar incidence of adverse events, including gastrointestinal effects, occurred in both groups. There was no suppression of antibody response in oseltamivir recipients.

CONCLUSION

Oral oseltamivir 75 mg once daily for 6 weeks effectively prevented clinical influenza in vaccinated frail older subjects using significant concomitant medications in a residential care setting. The treatment was well tolerated and provided additional protection to that afforded by vaccination.

Oseltamivir: a review of its use in influenza

Oseltamivir is a prodrug of oseltamivir carboxylate (Ro 64-0802, GS4071), a potent and selective inhibitor of the neuraminidase glycoprotein essential for replication of influenza A and B viruses. Studies in volunteers with experimental human influenza A or B showed that administration of oral oseltamivir 20 to 200 mg twice daily for 5 days reduced both the quantity and duration of viral shedding compared with placebo. Subsequent assessment of the drug at a dosage of 75 mg twice daily for 5 days in otherwise healthy adults with naturally acquired febrile influenza showed that oseltamivir reduced the duration of the disease by up to 1.5 days and the severity of illness by up to 38% compared with placebo when initiated within 36 hours of symptom onset (earlier initiation of therapy was associated with faster resolution). The incidence of secondary complications and the use of antibacterials were also reduced significantly in oseltamivir recipients. A liquid formulation of oseltamivir (2 mg/kg twice daily for 5 days) has been shown to be effective in the treatment of children with influenza, and data presented in abstracts suggest that the drug may also be of use in high-risk populations such as the elderly or those with chronic cardiac or respiratory disease. In addition to treatment efficacy, the drug has demonstrated efficacy when used for seasonal or household prophylaxis. Oral oseltamivir (75 mg once or twice daily for 6 weeks) during a period of local influenza activity significantly prevented the development of naturally acquired influenza by >70% compared with placebo in unvaccinated otherwise healthy adults. The drug also demonstrated efficacy when used adjunctively in previously vaccinated high-risk elderly patients (92% protective efficacy). Short term administration of oseltamivir (75 mg once daily for 7 days) may significantly reduce the risk of illness in household contacts of infected persons when administered within 48 hours of symptom onset in the infected person. Oseltamivir 75 mg twice daily for 5 days was well tolerated in clinical trials in healthy adults and high-risk patients, with nausea and vomiting being the most commonly reported events. Gastrointestinal events were mild and transient and both nausea and vomiting were less likely when oseltamivir was taken with food.

CONCLUSIONS

Oseltamivir is a well tolerated orally active neuraminidase inhibitor which significantly reduces the duration of symptomatic illness and hastens the return to normal levels of activity when initiated promptly in patients with naturally acquired influenza. It therefore represents a useful therapeutic alternative to zanamivir (especially in patients who prefer oral administration or who have an underlying respiratory disorder) and the M2 inhibitors amantadine and rimantadine (because of its broader spectrum of anti-influenza activity and lower likelihood of resistance) in patients with influenza. In addition, although annual vaccination remains the best means of influenza prevention, there may be a place for oseltamivir in providing household prophylaxis or adjunctive prophylaxis in high-risk vaccinated patients during an outbreak of the disease or for use in patients in whom vaccination is unsuitable or ineffective.