An Introduction To Epidemiologic Methods
Michele Kiely in Reproductive and Perinatal Epidemiology, 2019
A second advantage of case-control study design occurs in the study of disease with a long latent period. The latent period is the period of time elapsing between exposure to a particular factor and development of health problems from such exposure. Some conditions, particularly cancer, may take 20 years to develop after sufficient exposure. A cohort study design would require assembling an exposed and nonexposed group and following both groups for a minimum of 20 years to determine those subjects who develop the outcomes related to the exposure. A case-control approach would allow estimation of the relationship between exposure and outcome in a much shorter time. Thus, in the study of rare diseases or diseases with long latent intervals the case-control approach allows more rapid determination of the answer to a research question in a simpler and cheaper way than the cohort approach.
Key Concepts in Infectious Disease Epidemiology
Leonhard Held, Niel Hens, Philip O’Neill, Jacco Wallinga in Handbook of Infectious Disease Data Analysis, 2019
Closely related to the incubation period is the latent period which measures the time from infection to when an infected individual becomes infectious (and can thus transmit the infection to others). Often, the beginning of these time periods are determined by the time of exposure to an infectious agent since this time may be hard to distinguish from the occurrence of infection. Similarly, the end of the latent period often coincides approximately with the onset of symptoms so that the latent and incubation periods may be very similar. Incubation periods differ substantially for many common viral infections, ranging from a few days for influenza to around a week for dengue infection, 1 to 2 months for mononucleosis, and a decade or more for HIV. The length of the latent period is crucial in determining the risk of the spread of an infection, and infected individuals may not be ascertained during this time period (whereas interventions to limit infectiousness are available once symptoms are apparent).
Communicable diseases
Kelvyn Jones, Graham Moon in Health, Disease and Society, 1987
In more detail, an individual is infected at a particular moment in time and this is followed by an incubation period in which there are no signs of disease but the infected agent is multiplying and developing within the host. The incubation period can vary from a few hours in bacterial dysentry, to months for hepatitis induced by blood transfusion, to many years in the so-called slow-virus diseases. A period of a few days is most common; for example, the incubation period of influenza is about two days, polio about nine days and rubella eighteen days. A part of the incubation period is known as the latent period and this refers to time during which there are no signs of disease and the host is not infective. At some stage the latent period comes to an end, the infectious period begins and the host is capable of transmission, but the incubation period may not yet have ended and there may still be no signs of the disease. During this infectious period the host may come into contact with a susceptible and this individual may be infected. The time between the signs of symptoms in the first and second individuals is known as the serial period.
Effectiveness of facemasks for opening a university campus in Mississippi, United States – a modelling study
Published in Journal of American College Health, 2022
C. Raina MacIntyre, Valentina Costantino, Linkan Bian, Cindy Bethel
Given the data are for informing the reopening of campus for the fall semester, we used current disease notification data from July 2020 with a hypothetical campus opening date of July 8th, 2020. The model is simulated for four months starting on July 8th 2020, and we started the epidemic with 6 infected people entering the MSU campus. This was estimated as a proportion of the total daily new notifications in the State two days later (July 10th) of 708, corresponding to the campus population representing 0.83% of the population of the whole state. The cases were distributed in the “latent, not infectious yet” compartment. The rest of the MSU population was considered susceptible. We considered the average latent period to last 5.2 days,10 of which the last two days before symptoms onset are considered infectious.9
Transmission dynamics and timing of key events for SARS-CoV-2 infection in healthcare workers
Published in Infectious Diseases, 2021
Ahmet Naci Emecen, Ecem Basoglu Sensoy, Edanur Sezgin, Buket Yildirim Ustuner, Salih Keskin, Neslisah Siyve, Saadet Goksu Celik, Gamze Bayrak, Nurcan Senturk Durukan, Ayse Coskun Beyan, Alp Ergor, Belgin Unal, Gul Ergor
Serial interval is the time between the symptom onsets of a primary case and a secondary case. It defines the time between the appearance of similar symptoms in successive generations. Incubation period is the time from infection to symptom onset. Along with the infectious period, both are key parameters in determining the control strategies for COVID-19. The exact timing of SARS-CoV-2 infection and/or symptom onset could not be observed precisely. Generally, real-life data provides a period of exposure times to viral pathogens causing respiratory infections and is often referred to as coarse data. Coarse data emerges when the exact value of the data lies in a subset of the complete data (in this study: period) that contains the exact value [12]. Taking the coarseness in our data into account, we censored the exposure intervals and the exact symptom onset dates with the possible left and right endpoints. The left endpoint of the exposure intervals was set at 3 days prior to symptom onset of the primary case for the pairs who had continuous contact with each other. It is generally considered that during the presymptomatic period, infected persons can be contagious for 1–3 days prior to symptom onset [13].
In-flight transmission cluster of COVID-19: a retrospective case series
Published in Infectious Diseases, 2020
Naibin Yang, Yuefei Shen, Chunwei Shi, Ada Hoi Yan Ma, Xie Zhang, Xiaomin Jian, Liping Wang, Jiejun Shi, Chunyang Wu, Guoxiang Li, Yuan Fu, Keyin Wang, Mingqin Lu, Guoqing Qian
We conducted a retrospective study focussed on the clinical characteristics of ten patients with COVID-19 successively admitted to Xiaoshan First People’s Hospital from 25th January to 8th February 2020, after travelling on the flight. Patients were diagnosed based on the National Health Commission of the People’s Republic of China and the WHO interim guidelines [9,10]. For the ten patients included in our study, there was no recognized exposure history during 14 days before this flight. The incubation period was defined as the time from the flight arrival to the onset of illness. Hospitalized days were defined as the time from admission to discharge. The study was reviewed and approved by the Medical Ethical Committees of Xiaoshan First people's Hospital (Approval NO: 2020-02). Written informed consent was waived due to the urgent need to collect clinical data on this emerging disease and due to entirely anonymized data making sure that individuals cannot be identified.
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