Reconstructing the household transmission of influenza in the suburbs of Tokyo based on clinical cases

Background Influenza is a public health issue that needs to be addressed strategically. The assessment of detailed infectious profiles is an important part of this effort. Household transmission data play a key role in estimating such profiles. We used diagnostic and questionnaire-based data on influenza patients at a Japanese clinic to estimate the detailed infectious period (as well as incubation period, symptomatic and infectious periods, and extended infectious period after recovery) and the secondary attack ratio (SAR) of influenza for households of various sizes based on a modified Cauchemez-type model. Results The data were from enrolled patients with confirmed influenza who were treated at the Hirotsu Clinic (Kawasaki, Japan) with a neuraminidase inhibitor (NAI) during six northern hemisphere influenza seasons between 2010 and 2016. A total of 2342 outpatients, representing 1807 households, were included. For influenza type A, the average incubation period was 1.43 days (95% probability interval, 0.03–5.32 days). The estimated average symptomatic and infective period was 1.76 days (0.33–4.62 days); the extended infective period after recovery was 0.25 days. The estimated SAR rose from 20 to 32% as household size increased from 3 to 5. For influenza type B, the average incubation period, average symptomatic and infective period, and extended infective period were estimated as 1.66 days (0.21–4.61), 2.62 days (0.54–5.75) and 1.00 days, respectively. The SAR increased from 12 to 21% as household size increased from 3 to 5. Conclusion All estimated periods of influenza type B were longer than the corresponding periods for type A. However, the SAR for type B was less than that for type A. These results may reflect Japanese demographics and treatment policy. Understanding the infectious profiles of influenza is necessary for assessing public health measures.

Reconstructing the household transmission of influenza in the suburbs of Tokyo based on clinical cases

BackgroundInfluenza is a public health issue that needs to be addressed strategically. The assessment of detailed infectious profiles is an important part of this effort. Household transmission data play a key role in estimating such profiles. We used diagnostic and questionnaire-based data on influenza patients at a Japanese clinic to estimate the detailed infectious period (as well as incubation period, symptomatic and infectious periods, and extended infectious period after recovery) and the secondary attack ratio (SAR) of influenza for households of various sizes based on a modified Cauchemez-type model.ResultsThe data were from enrolled patients with confirmed influenza who were treated at the Hirotsu Clinic (Kawasaki, Japan) with a neuraminidase inhibitor (NAI) during six northern hemisphere influenza seasons between 2010 and 2016. A total of 2,342 outpatients, representing 1,807 households, were included. For influenza type A, the average incubation period was 1.43 days (95% probability interval: 0.03-5.32 days). The estimated average symptomatic and infective period was 1.76 days (0.33-4.62 days); the extended infective period after recovery was 0.25 days. The estimated SAR rose from 20% to 32% as household size increased from 3 to 5. For influenza type B, the average incubation period, average symptomatic and infective period, and extended infective period were estimated as 1.66 days (0.21-4.61), 2.62 days (0.54-5.75) and 1.00 days, respectively. The SAR increased from 12% to 21% as household size increased from 3 to 5.ConclusionAll estimated periods of influenza type B were longer than the corresponding periods for type A. However, the SAR for type B was less than that for type A. These results may reflect Japanese demographics and treatment policy. Understanding the infectious profiles of influenza is necessary for assessing public health measures.

Analysis of Covid-19 Data for Eight European Countries and the United Kingdom Using a Simplified SIR Model

Background: As the SARS-Cov-2/Covid-19 pandemic continues to ravage the world, it is important to understanding the characteristics of its spread and possible correlates for control to develop strategies of response. Methods: Here we show how a simple Susceptible-Infective-Recovered (SIR) model applied to data for eight European countries and the United Kingdom (UK) can be used to forecast the descending limb (post-peak) of confirmed cases and deaths as a function of time, and predict the duration of the pandemic once it has peaked, by estimating and fixing parameters using only characteristics of the ascending limb and the magnitude of the first peak. Results: The predicted and actual case fatality ratio, or number of deaths per million population from the start of the pandemic to when daily deaths number less than five for the first time, was lowest in Norway (predicted: 44 5 deaths/million; actual: 36 deaths/million) and highest for the United Kingdom (predicted: 578 +/- 65 deaths/million; actual 621 deaths/million). The inferred pandemic characteristics separated into two distinct groups: those that are largely invariant across countries, and those that are highly variable. Among the former is the infective period, TL = 16.3 2.7 days, the average time between contacts, TR = 3.8+/- 0.5 days and the average number of contacts while infective R = 4.4 +/- 0.5. In contrast, there is a highly variable time lag TD between the peak in the daily number of confirmed cases and the peak in the daily number of deaths, ranging from lows of TD = 2,4 days for Denmark and Italy respectively, to highs of TD = 12, 15 for Germany and Norway respectively. The mortality fraction, or ratio of deaths to confirmed cases, was also highly variable, ranging from low values 3%, 5% and 5% for Norway, Denmark and Germany respectively, to high values of 18%, 20% and 21% for Sweden, France, and the UK respectively. The probability of mortality rather than recovery was a significant correlate of the duration of the pandemic, defined as the time from 12/31/2019 to when the number of daily deaths fell below 5. Finally, we observed a small but detectable effect of average temperature on the probability of infection per contact, with higher temperatures associated with lower infectivity. Conclusions: Our simple model captures the dynamics of the initial stages of the pandemic, from its exponential beginning to the first peak and beyond, with remarkable precision. As with all epidemiological analyses, unanticipated behavioral changes will result in deviations between projection and observation. This is abundantly clear for the current pandemic. Nonetheless, accurate short-term projections are possible, and the methodology we present is a useful addition to the epidemiologist's armamentarium. Our predictions assume that control measures such as lockdown, social distancing, use of masks etc. remain the same post-peak as before peak. Consequently, deviations from our predictions are a measure of the extent to which loosening of control measures have impacted case-loads and deaths since the first peak and initial decline in daily cases and deaths. Our findings suggest that the two key parameters to control and reduce the impact of a developing pandemic are the infective period and the mortality fraction, which are achievable by early case identification, contact tracing and quarantine (which would reduce the former) and improving quality of care for identified cases (which would reduce the latter).

Reconstructing the Household Transmission of Influenza in the Suburbs of Tokyo Based on Clinical Cases

Background Influenza is a public health issue that needs to be addressed strategically and assessment of detailed infectious profiles is important for that. Household transmission data have played a key role for estimating these profiles. From one clinic’s influenza diagnostic and questionnaire-based data, we aimed to estimate the detailed infectious period (incubation, symptomatic and infective, and extended infective after recovery) and secondary attack ratio (SAR) for each household size of influenza by using modified Cauchemez-type model.Results The data source was derived from enrolled patients with confirmed influenza who were treated at the Hirotsu Clinic (Kawasaki, Japan) with a neuraminidase inhibitor (NAI) during the 6 Northern Hemisphere influenza seasons between 2010 and 2016. A total of 2,342 outpatients representing 1,807 households were included. For influenza type A, average incubation period and its 95% probability interval was 1.43 (0.03-5.32) days. Estimated average symptomatic and infective period was 1.76 (0.33-4.62) days and point estimated extended infective period after recovery was 0.25 days. Estimated SAR elevated from 20% to 32% as household size increases from 3 to 5. For influenza type B, average incubation period, average symptomatic and infective period, and extended infective period were estimated 1.66 (0.21-4.61) days, 2.62 (0.54-5.75) days and 1.00 days, respectively. SAR was increased 12% to 21% as household size increases from 3 to 5.Conclusion All estimated periods of influenza type B were longer than those of influenza type A. On the other hands, SAR of type B was less than that of type A. These results may reflect Japanese demographics and treatment policy. It is useful to understand the infectious profiles of influenza for examining public health measures.

The basics of infection microbiology

This chapter outlines the natural history of infections caused by a variety of organisms. These organisms may already colonize a patient (endogenous) or come from another source (exogenous). They vary in the time it takes to cause symptoms (incubation period). Some are more infective than others, and the infective period varies depending on the organism. A range of diagnostic methods are used to identify the disease, from growing the organism (culture) to using molecular techniques to identify characteristics unique to the organism. Understanding what is causing an infection is important in public health management to support outbreak identification and management. Advanced techniques can identify whether the organism is likely to be transmitted from one individual to another. Antimicrobial resistance is becoming more and more problematic and can lead to difficulties of treatment of even simple infections.

Comparison and Contrast of the Elimination Campaigns for Poliomyelitis and Leprosy: Which is More Feasible?

As we approach the third decade since the WHO started addressing the eradication of poliomyelitis and leprosy, a reflection of the previous campaigns efficacy and an evaluation of further elimination feasibility is important to adapt and intensify the next steps. We performed a critical review of the poliomyelitis and leprosy eradication campaigns to evaluate their technical and operational feasibilities. Vaccination and active case search are highly effective tools against poliomyelitis. If political stability and good vaccination coverage is achieved, poliomyelitis will be an easy target for eradication. Leprosy, on the other hand, faces many barriers towards elimination. The lack of a high efficacy vaccine, the long asymptomatic but infective period, the lack of screening tests and a poorly established elimination target, prevents this disease from being eliminated. In a world where resources and funding are limited, it is apparent that poliomyelitis is a more feasible target for elimination than leprosy.

Effects of temperature on survival, infectivity and in vitro encystment of the cercariae of Echinostoma caproni

The effects of temperature on survival, infectivity and in vitro encystment of Echinostoma caproni cercariae in artificial spring water (ASW) were studied. Effects of aging cercariae in ASW at various temperatures showed that at 23°C cercariae achieved 50% survival in 24 h, compared to 92 h at 12°C. Cercariae aged in ASW at 28 and 37.5°C showed 50% survival at 16 and 10 h, respectively. Cercariae aged at different temperatures for various times were used to infect juvenile Helisoma trivolvis (Colorado strain) snails maintained in ASW at 23°C. Index of infectivity was based on counting encysted metacercariae in the snails at 8 to 12 h post-infection. Cercariae aged at 23, 28 and 37.5°C showed 50% encystment at 6, 8 and 4 h, respectively. Cercariae aged at 4°C showed 50% encystment in 10 h and cercariae aged at 12°C showed 50% encystment beyond 16 h. Cercariae showed maximal longevity and infectivity in snails when aged at 12°C in ASW. For E. caproni, as in other digeneans, the infective period of cercariae is markedly shorter than the maximal life-span at any given temperature. Studies on in vitro encystment of E. caproni cercariae in Locke's solution:ASW (1:1) showed that encystment was optimal at 23°C (78% encystment) and that it declined to 44% at 28°C and became almost nil (0.02%) at 12 or 37.5°C.

Survival and infectivity of Hypoderaeum conoideum and Euparyphium albuferensis cercariae under laboratory conditions

The survival characteristics of the cercariae of Hypoderaeumconoideum and Euparyphiumalbuferensis (Trematoda: Echinostomatidae) at 20°C and 30°C are described, and the age dependency of their infectivity at 20°C is studied to determine their respective transmission efficiencies. Cercarial survival was found to be age-dependent and was higher at 20°C. For both cercariae, the maximum life-span was 26 h at 20°C and 16 h at 30°C, and their respective times to 50% mortality were similar at each temperature. Both cercariae seem to be well adapted to transmission in their natural habitat, though cercarial infectivity of H. conoideum was higher than that of E. albuferensis, this being correlated with their prevalences in nature. The age-dependency of cercarial survival may be related to steadily diminishing endogenous energy levels, though the delay in attaining maximum infectivity suggests that other factors not related to energy considerations are involved in the delimitation of the cercarial infective period. However, this latter observation may constitute an adaptative mechanism allowing cercarial dissemination.

Effects of temperature and host density on the snail-finding capacity of cercariae of Echinostoma caproni (Digenea: Echinostomatidae)

The effect of temperature (19–36 °C) and snail host density (0.014–10 snails/1) on the snail-finding capacity of Echinostoma caproni cercariae is described. The initial swimming speed increased whereas the length of the infective period decreased with increasing temperature. The combined effect resulted in the E. caproni cercarial snail-finding capacity being temperature independent in the range 19 to 36 °C at a snail density of 0·014 snails/1. A moderate temperature dependency was, however, seen at a lower snail density. The cercarial snail-finding capacity was snail-host density dependent in the density range 0.014 to 1 snail/1. The findings from this study show that a relatively low and biologically realistic snail host density must be used in experimental studies if realistic estimates of the dynamics of cercarial transmission are to be obtained.

Parasitic development of the mermithid nematode Reesimermis nielseni in the larval mosquito Aedes aegypti

Newly hatched Aedes aegypti larvae were experimentally infected with controlled levels of infection of the mermithid nematode Reesimermis nielseni and the development of the parasite was recorded. The nematode increased in length by 18-fold and in width by 16-fold during a relatively short 6- to 8-day parasitic phase. Most of the nematode's growth was restricted to the latter half (3 days) of the infective period. A cuticularized tube, extending posteriorly from the stoma, was present throughout parasitic development. After 3 days infection, the nematode possessed a membrane-bound stichosome containing 16 stichocytes, and a cellular trophosome with storage nutrient granules beginning to accumulate in the intercellular spaces. Between 3 and 4 days infection, the parasite probably molted as its growth rate suddenly increased, its stylet was lost, and a caudal appendage acquired. The stichosome, trophosome, and genital rudiment continued to develop for the rest of the infective period. A discrete granular body of unknown function and containing a large nucleated cell developed anterior to the stichosome. By the 5th and 6th days of infection, the enlarged trophosome, packed with storage globules, almost completely obscured the stichosome and genital rudiment. The nematode does not possess a stylet to facilitate emergence from its host, nor does it appear to molt immediately before emergence. The possible functions of the stichosome and cuticularized tube are discussed.