Across decades of co-circulation in humans, influenza A subtypes H1N1 and H3N2 have caused seasonal epidemics characterized by different age distributions of cases and mortality. H3N2 causes the majority of severe, clinically attended cases in high-risk elderly cohorts, and the majority of overall deaths, whereas H1N1 causes fewer deaths overall, and cases shifted towards young and middle-aged adults. These contrasting age profiles may result from differences in childhood imprinting to H1N1 and H3N2 or from differences in evolutionary rate between subtypes. Here we analyze a large epidemiological surveillance dataset to test whether childhood immune imprinting shapes seasonal influenza epidemiology, and if so, whether it acts primarily via homosubtypic immune memory or via broader, heterosubtypic memory. We also test the impact of evolutionary differences between influenza subtypes on age distributions of cases. Likelihood-based model comparison shows that narrow, within-subtype imprinting shapes seasonal influenza risk alongside age-specific risk factors. The data do not support a strong effect of evolutionary rate, or of broadly protective imprinting that acts across subtypes. Our findings emphasize that childhood exposures can imprint a lifelong immunological bias toward particular influenza subtypes, and that these cohort-specific biases shape epidemic age distributions. As a consequence, newer and less "senior" antibody responses acquired later in life do not provide the same strength of protection as responses imprinted in childhood. Finally, we project that the relatively low mortality burden of H1N1 may increase in the coming decades, as cohorts that lack H1N1-specific imprinting eventually reach old age.

No abstract

Objectives Respiratory syncytial virus (RSV) is a common cause of respiratory illness, health care visits, and hospitalizations. Arizona, which began conducting laboratory surveillance in 2004, has noted an increase in RSV cases (defined as a laboratory-positive result) among adults aged ≥65, concurrent with increasing reports from polymerase chain reaction (PCR) testing. We assessed whether the shift in the age distribution of reported RSV cases resulted from a change in RSV testing practices. Methods We used data on laboratory-confirmed RSV cases reported during 2013-2017 from the statewide surveillance system to assess the frequency of test types (rapid antigen, immunofluorescence assay, PCR, and viral culture) by age groups across RSV seasons, and we used logistic regression to estimate changes in odds of receiving a PCR test. We used statewide emergency department hospital discharge data for the same period to assess testing practices regardless of test result. Results The overall proportion of PCR tests among RSV cases increased significantly, from 22% in 2013 to 55% in 2017 ( P < .001). The percentage of RSV cases among adults aged ≥65 also increased significantly, from 4% in 2013 to 11% in 2017 ( P < .001) of RSV cases. Adults aged ≥65 had more than 8 times the odds of positive PCR results than children aged <5, both in crude (odds ratio [OR] = 8.8; 95% CI, 7.6-10.2) and season-adjusted (adjusted OR = 8.1; 95% CI, 7.0-9.5) models. Hospital discharge data corroborated increased RSV PCR usage from 2013 to 2017. Conclusion Increasing RSV rates among adults aged ≥65 are likely a result of changes in testing practices. This age group may need more targeted intervention and future vaccination.

This study is a follow-up observational study to assess the prevalence of chlamydia (CT) and gonorrhea (GC) among women who undergo a first-trimester surgical termination in a large public, urban hospital-based termination clinic, and to compare the rates to previously published data. We conducted a retrospective chart review on 4197 patients who underwent CT and GC testing before an elective, first-trimester surgical termination between 1 June 2014 and 31 May 2015. The prevalence rates were calculated and compared by chi square tests to previously published data from 1 January 2006 to 30 June 2006 from the same publicly-funded pregnancy termination clinic. Our study population comprised mostly of African Americans (86.8%), and more than half were aged less than 25 years. The overall prevalence of CT in our population was 9.6%, which was significantly different to the prevalence of 11.4% in 2006 ( p value = 0.03). The overall prevalence of GC in our population was 1.9%, which was not significantly different to the prevalence of 2.6% in 2006. To conclude, this study demonstrates the high prevalence rate of CT-positive and GC-positive patients in our publicly-funded pregnancy termination clinic. The prevalence of infection with CT and GC in our study is higher than in other family planning clinics. Regular screening of all patients who undergo induced termination in pregnancy termination clinics can provide a valuable opportunity for physicians to counsel patients about sexually transmitted infection prevention and treatment prior to the procedure or distribution of medications.

Despite decreasing incidence, HIV is the leading cause of morbidity and mortality in Kenya. In Kisumu, HIV prevalence is ∼19% and incidence is second highest in the country. There is a need to identify HIV-positive persons and link them to care. Universal testing in healthcare facilities is a strategy supported by the Kenyan government to facilitate identification of new HIV cases. The objective was to identify patterns of HIV testing in a hospital in Kisumu, Kenya, a setting where universal testing is recommended. A retrospective chart review of patients seen between January 2014 and December 2014 was conducted. We collected information on 5% of admitted patients older than 18 years of age. Chi square analysis characterized patients and Poisson regression modeling produced the relative risk of being tested. In 2014, 9071 patients were admitted from the emergency unit. From the sample, 24% of patients were recorded to have been tested for HIV. There was no significant difference in testing between genders (p = 0.99). Females with a genitourinary diagnosis were significantly more likely to be tested for HIV than other diagnoses (adjusted relative risk [aRR] = 1.79). Males with an infectious disease were 1.86 times more likely to be tested for HIV than other diagnoses, while females with pregnancy-related diagnoses were 50% less likely to be tested for HIV (aRR = 0.50). While universal testing supports a non-risk-based screening of patients, higher risk diagnoses were more likely to be tested. This study demonstrates that there is still opportunity to further practice and implement universal testing.