Influenza ( Flu )- and respiratory syncytial virus-associated morbidity and mortality in the nursing home population.

OBJECTIVES: To estimate winter viral-related morbidity and mortality in Tennessee nursing home residents during 4 consecutive years. DESIGN: A retrospective cohort study. SETTING: Three hundred eighty-one Tennessee nursing homes. PARTICIPANTS: Nursing home residents. MEASUREMENTS: Viral surveillance data were used to define three seasons: influenza ( flu ) (influenza ( flu ) and respiratory syncytial virus (RSV) cocirculating), RSV (RSV alone circulating), and non winter-viral (neither virus circulating). Adjusted seasonal differences in rates of cardiopulmonary hospitalizations, antibiotic prescriptions, and deaths during these three seasons were calculated to estimate annual hospitalizations, courses of antibiotics, and deaths attributable to influenza ( flu ) and RSV from 1995 to 1999. RESULTS: Nursing home residents had 81,885 person-years of follow-up. In the 63% of residents with comorbid conditions that increase influenza ( flu ) morbidity, influenza ( flu ) infection contributed to an estimated average of 28 hospitalizations, 147 courses of antibiotics, and 15 deaths per 1,000 persons annually. Similarly, RSV accounted for an annual average of 15 hospitalizations, 76 courses of antibiotics, and 17 deaths per 1,000 persons. Influenza ( Flu ) and RSV accounted for 7% of cardiopulmonary hospitalizations and 9% of total deaths in high-risk residents during the 4 study years. Absolute morbidity and mortality were lower in residents without identified comorbid conditions but accounted for 15% of hospitalizations and 14% of deaths. These estimates depend on the assumption that morbidity and mortality from other respiratory viruses were distributed evenly between the three defined seasons. CONCLUSION: Influenza ( Flu ) and RSV substantially increased hospitalization rates, antibiotic use, and deaths in elderly nursing home residents each winter. These data should encourage persistent efforts toward disease prevention, and thoughtful study of vaccine development and delivery, diagnostic tools, and methods of prophylaxis and therapy.

Influenza ( Flu ) virus can enter and infect cells in the absence of clathrin-mediated endocytosis.

Influenza ( Flu ) virus has been described to enter host cells via clathrin-mediated endocytosis. However, it has also been suggested that other endocytic routes may provide additional entry pathways. Here we show that influenza ( flu ) virus may enter and infect HeLa cells that are unable to take up ligands by clathrin-mediated endocytosis. By overexpressing a dominant-negative form of the Eps15 protein to inhibit clathrin-mediated endocytosis, we demonstrate that while transferrin uptake and Semliki Forest virus infection were prevented, influenza ( flu ) virus could enter and infect cells expressing Eps15Delta95/295. This finding is supported by the successful infection of cells with influenza ( flu ) virus in the presence of chemical treatments that block endocytosis, namely, chlorpromazine and potassium depletion. We show also that influenza ( flu ) virus may infect cells incapable of uptake by caveolae. Treatment with the inhibitors nystatin, methyl-beta-cyclodextrin, and genistein, as well as transfection of cells with dominant-negative caveolin-1, had no effect on influenza ( flu ) virus infection. By combining inhibitory methods to block both clathrin-mediated endocytosis and uptake by caveolae in the same cell, we demonstrate that influenza ( flu ) virus may infect cells by an additional non-clathrin-dependent, non-caveola-dependent endocytic pathway. We believe this to be the first conclusive analysis of virus entry via such a non-clathrin-dependent pathway, in addition to the traditional clathrin-dependent route.

Influenza ( Flu ) surveillance

From 1982 to June 1990, seven influenza ( flu ) A (H3N2) epidemics and four influenza ( flu ) A (H1N1) epidemics occurred in Shanghai, and several new variants of influenza ( flu ) virus were isolated. During that period, influenza ( flu ) A (H3N2) and influenza ( flu ) A (H1N1) appeared alternatively while each lasted for one to two years. The epidemic peak of influenza ( flu ) usually was seen from July to August and late winter to early spring. The subtype which appears in July and August usually starting in late winter and early spring in Shanghai causes epidemics in the northern regions of China and some other countries in the northern hemisphere. If minor epidemics occur only in July and August, further antigenic changes may cause moderate epidemics in late winter and next early spring. Information supplied for prediction of influenza ( flu ) epidemics and timely preparation of new vaccines may lead to better control of influenza ( flu ).

Varying nature of the cell receptors for influenza ( flu ) and para-influenza ( flu ) viruses

A comparative study of receptors for influenza ( flu ) virus, fowl plague virus, and human parainfluenza ( flu ) type 3 virus was carried out. Natural receptors of guinea pig erythrocytes were destroyed with neuraminidase, and individual gangliosides GM1, GD1a, and GT1b were inserted into their membranes. The labeled virus was adsorbed on the erythrocytes modified in this manner, and the degree of restoration of the receptor activity of erythrocytes lost after neuraminidase treatment was determined. Two gangliosides, GD1a and GT1b, were found to be capable of functioning as specific receptors for influenza ( flu ) virus. Both gangliosides restored completely the virus adsorption on erythrocytes. In contrast, none of the three gangliosides used did not restore parainfluenza ( flu ) virus adsorption. It is concluded that the nature of influenza ( flu ) and parainfluenza ( flu ) virus receptors is different.

Evaluation of a rapid optical immunoassay for influenza ( flu ) viruses (FLU OIA test) in comparison with cell culture and reverse transcription-PCR.

The FLU OIA test was evaluated with 146 throat swab specimens from subjects with a flu-like illness in six Canadian clinics during the 1999-2000 flu season. The rate of positivity of the FLU OIA test (41.5%) was significantly lower than that of cell culture (55.2%) or reverse transcription-PCR (55.9%) during a season in which only influenza ( flu ) A virus was detected.

The etiological structure of the morbidity from influenza ( flu ) and other ARDs on the territory of Russia in the season of 1997-1998

The antigenic properties of 51 strains of influenza ( flu ) virus A(H1N1), isolated in different cities of Russia during the epidemic of 1998, were studied. Most of these strains (49) proved to be similar to virus A/Bern/07/95 in the antigenic structure of hemagglutinin, but 2 strains isolated in Ulan-Ude were found to be closely related to new antigenic variants of this virus: A/Beijing/262/95 and A/Fukuoka/c7/98. The analysis of the antigenic structure of influenza ( flu )-like diseases (ILD) in different cities of Russia revealed that adenoviruses causing up to 10.9-14.6% of all acute respiratory virus infections dominated at the pre- and post-epidemic periods. RS-viruses, parainfluenza ( flu ) viruses of types 2 and 3 circulated during the whole season (their proportion was 5.1-6.6%). The intensity of the circulation of influenza ( flu ) viruses A(H1N1) and A(H3N2) increased, starting from January, and continued till April 1998; its peak was observed in February-March in most of the cities of Russia (up to 37.5-41.6% according to the results of immunofluorescent diagnostics and 53-73% of ILD according to the results of the hemagglutination inhibition test). The occurrence of influenza ( flu ) B during this season was very low.

Induction of antibody responses to influenza ( flu ) virus in human lymphocyte cultures. I. Role of interleukin 2.

The in vitro T cell-dependent antibody response of human lymphocytes to influenza ( flu ) virus X31 was used to study the role of T cell-derived lymphokines in antigen-specific responses. Supernatant from cultures of phytohaemagglutinin-stimulated, pooled human tonsil cells (PHA-MLR) was capable of replacing T cells and inducing T-depleted tonsil cells to secrete influenza ( flu )-specific antibody. The T cell-replacing activity of PHA-MLR supernatant co-purified with interleukin 2 (IL 2) on Ultrogel AcA54 gel filtration and reversed phase-high performance liquid chromatography. PHA-MLR supernatant and IL 2 also enhanced B cell proliferation induced by anti-mu or Staphylococcal aureus strain Cowan I (SAC). A murine monoclonal antibody directed against the human IL 2 receptor (Mab 2A3) was used to completely block the enhancement of influenza ( flu )-specific antibody production mediated by PHA-MLR supernatant, purified IL 2, and recombinant human IL 2. Mab 2A3 did not affect the T-independent B cell proliferation induced by anti-mu or SAC, but abrogated the enhancing effect of the PHA-MLR supernatant and IL 2 in this culture system. Immunofluorescence studies failed to demonstrate binding of Mab 2A3 to B cells activated by the X31 influenza ( flu ) virus and IL 2, or by SAC. By using Mab 2A3 to mask out IL 2 effects in the influenza ( flu )-specific culture system, no other B cell differentiating activities were revealed in supernatants from lymphocytic cultures stimulated with a variety of mitogens. Thus, our results indicate that the production of influenza ( flu )-specific antibodies by T-depleted human lymphocyte cultures is absolutely dependent on the presence of both antigen and IL 2.

Comparative analysis of evolutionary mechanisms of the hemagglutinin and three internal protein genes of influenza ( flu ) B virus: multiple cocirculating lineages and frequent reassortment of the NP, M, and NS genes.

Phylogenetic profiles of the genes coding for the hemagglutinin (HA) protein, nucleoprotein (NP), matrix (M) protein, and nonstructural (NS) proteins of influenza ( flu ) B viruses isolated from 1940 to 1998 were analyzed in a parallel manner in order to understand the evolutionary mechanisms of these viruses. Unlike human influenza ( flu ) A (H3N2) viruses, the evolutionary pathways of all four genes of recent influenza ( flu ) B viruses revealed similar patterns of genetic divergence into two major lineages. Although evolutionary rates of the HA, NP, M, and NS genes of influenza ( flu ) B viruses were estimated to be generally lower than those of human influenza ( flu ) A viruses, genes of influenza ( flu ) B viruses demonstrated complex phylogenetic patterns, indicating alternative mechanisms for generation of virus variability. Topologies of the evolutionary trees of each gene were determined to be quite distinct from one another, showing that these genes were evolving in an independent manner. Furthermore, variable topologies were apparently the result of frequent genetic exchange among cocirculating epidemic viruses. Evolutionary analysis done in the present study provided further evidence for cocirculation of multiple lineages as well as sequestering and reemergence of phylogenetic lineages of the internal genes. In addition, comparison of deduced amino acid sequences revealed a novel amino acid deletion in the HA1 domain of the HA protein of recent isolates from 1998 belonging to the B/Yamagata/16/88-like lineage. It thus became apparent that, despite lower evolutionary rates, influenza ( flu ) B viruses were able to generate genetic diversity among circulating viruses through a combination of evolutionary mechanisms involving cocirculating lineages and genetic reassortment by which new variants with distinct gene constellations emerged.

Development of real-time RT-PCR for the detection of avian influenza ( Flu ) virus.

A real-time reverse transcriptase/polymerase chain reaction (RRT-PCR) assay was developed using hydrolysis probes for the detection of avian influenza ( Flu ) virus (AIV) and the H5 and H7 subtypes. The AIV specific primers and probes were directed to regions of the AIV matrix gene that are conserved among most type A influenza ( flu ) viruses. The H5 and H7 primers and probes are directed to H5 and H7 hemagglutinin gene regions that are conserved among North American avian influenza ( Flu ) viruses. The sensitivity and specificity of this RRT-PCR assay was compared to virus isolation (VI) in chicken embryos with 1550 clinical swab samples from 109 live-bird markets (LBMs) in New York and New Jersey. RRT-PCR detected influenza ( flu ) in samples from 61 of 65 (93.8%) of the LBMs that were the sources of VI positive samples. Of the 58 markets that were positive for H7 influenza ( flu ) by hemagglutination inhibition assay, RRT-PCR detected H7 influenza ( flu ) in 56 markets (96.5%). Too few H5 positive samples were obtained to validate the H5 RRT-PCR assay in this study. Although RRT-PCR was less sensitive than VI on an individual sample basis, this study demonstrated that the AIV and H7 RRT-PCR assays are good tools for the rapid screening of flocks and LBMs.

Interleukin-6 production by endothelial cells after infection with influenza ( flu ) virus and cytomegalovirus.

Inflammation plays a role in the pathogenesis of cardiovascular diseases. Viruses may be a cause of chronic inflammation, and both influenza ( flu ) virus and CMV have been associated with cardiovascular diseases. IL-6, a proinflammatory cytokine with antiviral effects, has a pivotal role in the immune response, and under pathologic conditions, prohemostatic effects of IL-6 could lead to pathologic thrombosis and vascular plaque instability. To investigate this role of IL-6, we measured the production of IL-6 by human endothelial cells after infection with influenza ( flu ) virus and CMV. After infection with influenza ( flu ) virus or CMV, IL-6 release into the medium increased (1756.5+/-156.9 pg/mL vs 284.4+/-55.3 pg/mL; P < .001) for influenza ( flu )-Infected compared with uninfected cells after 36 hours' incubation. Ultracentrifuged influenza ( flu ) virus supernatants, heat-inactivated virus, and purified hemagglutinin were not able to elicit IL-6 synthesis by human endothelial cells. These findings show that CMV and influenza ( flu ) virus are capable of modulating the in vitro production of IL-6, a cytokine involved in vascular inflammation, by human endothelial cells.