[Effect of the time between symptom onset, swabbing and testing on the detection of influenza virus]. / Influencia de los tiempos entre el inicio de síntomas, la toma de frotis nasofaríngeo y su procesamiento en laboratorio en la detección de gripe.

BACKGROUND: Influenza surveillance requires the collection of nasopharyngeal swabs in Primary Care for testing in reference laboratories. We evaluated the influence on the laboratory results of the time since the onset of symptoms to swabbing (TSS) and from then until laboratory processing (TSL). METHODS: We analysed swabs collected in the Sentinel Network of Navarra during the 2009-2010 influenza season. The samples were kept refrigerated until analysed by RT-PCR and viral culture. We analysed the percentage of positive swabs to influenza virus in accordance with the TSS and TSL by logistic regression. RESULTS: From a total of 937 swabs, 373 (40%) were positive for influenza by RT-PCR. The TSS ranged from 0-15 days. In the adjusted analysis by period, laboratory and age, having a positive influenza culture decreased to less than half when the TSS was 4-5 days (OR=0.47; 95% CI, 0.24-0.94), and having a positive RT-PCR decreased when the TSS was 5 days or more (OR=0.24, 95% CI, 0.09-0.65). TSL does not significantly affect the result of the RT-PCR (OR by each day=0.96; 95% CI, 0.88-1.04), or the result of the viral culture (OR by each day=0.97, 95% CI, 0.89-1.06). CONCLUSIONS: A TSS over 3 days reduced the likelihood of confirmation of influenza, affecting the viral culture more than the RT-PCR. A TSL within a range of two weeks had no significant effect on the results of the RT-PCR or the viral culture.

Vaccine effectiveness in preventing influenza hospitalizations in Navarre, Spain, 2010-2011: cohort and case-control study.

We evaluated the 2010-2011 seasonal influenza vaccine effectiveness in preventing hospitalizations. Using healthcare databases we defined the target population for vaccination in Navarre, Spain, consisting of 217,320 people with major chronic conditions or aged 60 years and older. All hospitalized patients with influenza-like illness (ILI) were swabbed for influenza testing. A total of 269 patients with ILI were hospitalized and 61 of them were found positive for influenza virus: 58 for A(H1N1)2009 and 3 for B virus. The incidence rates of hospitalization with laboratory-confirmed influenza were compared by vaccination status. In the Cox regression model adjusted for sex, age, children in the household, urban/rural residence, comorbidity, pandemic vaccination, pneumococcal vaccination, outpatient visits and hospitalization in the previous year, the seasonal vaccine effectiveness was 58% (95% CI: 16-79%). The nested test-negative case-control analysis gave an adjusted estimate of 59% (95% CI: 4-83%). These results suggest a moderate effect of the 2010-2011 seasonal influenza vaccine in preventing hospitalization in a risk population. The close estimates obtained in the cohort and the test-negative case-control analyses suggest good control of biases.

[Differences between summer and fall waves of influenza in the pandemic of influenza (H1N1) 2009 in Navarre, Spain]. / Diferencias entre las ondas gripales de verano y de otoño durante la pandemia de gripe (H1N1) 2009 en Navarra.

BACKGROUND: Two waves of influenza (H1N1) 2009 were produced in Navarre in 2009, one in the summer and the other in the fall. We aim to compare the characteristics of the two epidemic waves. METHODS: We analysed individual influenza reports, virological confirmations in the primary care sentinel network, and hospitalised cases with confirmed influenza in Navarre. We compared the summer period (week 21 to 39 in 2009) with the fall-winter period (week 40 in 2009 to 20 in 2010). RESULTS: Two waves of influenza A(H1N1)2009 occurred during 2009, with peaks in July and November. In the summer (week 21 to 39) 4389 cases of influenza syndrome were reported, with young adults the most affected group (58% aged 15-44 years). The highest incidence was registered after the San Fermin fiesta (92 cases per 100,000 population in week 29), with immediate return to baseline levels. A second wave occurred in the fall, with rates up to 7 times higher (667 cases per 100,000 in week 45); they remained above the epidemic threshold for 9 weeks, with children aged 5-14 years (111 per 1000) the most affected group. In the peak of both waves the percentage of smears confirmed for influenza reached 60%. During the summer there were 66 admissions with confirmed influenza (H1N1) 2009, and 158 than in the fall. The proportion of cases requiring admission to hospital was higher in the summer (1.5%) than in fall (0.8%: p<0,0001). CONCLUSION: Influenza circulation was much lower in the summer. Serious cases occurred in periods of both high and low incidence of influenza syndromes.

Effectiveness of the monovalent influenza A(H1N1)2009 vaccine in Navarre, Spain, 2009-2010: cohort and case-control study.

We defined a population-based cohort (596,755 subjects) in Navarre, Spain, using electronic records from physicians, to evaluate the effectiveness of the monovalent A(H1N1)2009 vaccine in preventing influenza in the 2009-2010 pandemic season. During the 9-week period of vaccine availability and circulation of the A(H1N1)2009 virus, 4608 cases of medically attended influenza-like illness (MA-ILI) were registered (46 per 1000 person-years). After adjustment for sociodemographic covariables, outpatient visits and major chronic conditions, vaccination was associated with a 32% (95% CI: 8-50%) reduction in the overall incidence of MA-ILI. In a test negative case-control analysis nested in the cohort, swabs from 633 patients were included, and 123 were confirmed for A(H1N1)2009 influenza. No confirmed case had received A(H1N1)2009 vaccine versus 9.6% of controls (p<0.001). The vaccine effectiveness in preventing laboratory-confirmed influenza was 89% (95% CI: 36-100%) after adjusting for age, health care setting, major chronic conditions and period. Pandemic vaccine was effective in preventing MA-ILI and confirmed cases of influenza A(H1N1)2009 in the 2009-2010 season.