It is less clear that a pure culture comes from an animal source serving as host than it is when derived from microbes derived from plate culture.Epidemiology, or the study and analysis of who, why and where disease occurs, and what determines whether various populations have a disease, is another important tool used to understand infectious disease. Epidemiologists may determine differences among groups within a population, such as whether certain age groups have a greater or lesser rate of infection; whether groups living in different neighborhoods are more likely to be infected; and by other factors, such as gender and race. Researchers also may assess whether a disease outbreak is sporadic, or just an occasional occurrence; endemic, with a steady level of regular cases occurring in a region; epidemic, with a fast arising, and unusually high number of cases in a region; or pandemic, which is a global epidemic. If the cause of the infectious disease is unknown, epidemiology can be used to assist with tracking down the sources of infection. Contagiousness
Infectious diseases are sometimes called contagious diseases when they are easily transmitted by contact with an ill person or their secretions (e.g., influenza). Thus, a contagious disease is a subset of infectious disease that is especially infective or easily transmitted. Other types of infectious, transmissible, or communicable diseases with more specialized routes of infection, such as vector transmission or sexual transmission, are usually not regarded as "contagious", and often do not require medical isolation (sometimes loosely called quarantine) of those affected.
Focal seizures (also called partial seizures and localized seizures) are seizures which affect initially only one hemisphere of the brain. The brain is divided into two hemispheres, each consisting of four lobes – the frontal, temporal, parietal and occipital lobes. A focal seizure is generated in and affects just one part of the brain – a whole hemisphere or part of a lobe. Symptoms will vary according to where the seizure occurs. When seizures occur in the frontal lobe the patient may experience a wave-like sensation in the head. When seizures occur in the temporal lobe, a feeling of déjà vu may be experienced. When seizures are localized to the parietal lobe, a numbness or tingling may occur. With seizures occurring in the occipital lobe, visual disturbances or hallucinations have been reported. Types
As of 2017, focal seizures are split into two main categories, focal onset aware, and focal onset impaired awareness. What was previously termed a secondary generalised seizure is now termed a focal to bilateral seizure.In focal onset aware seizures, a small part of one of the lobes may be affected and the person remains conscious. This can often be a precursor to a larger focal onset impaired awareness seizure. When this is the case, the focal aware seizure is usually called an aura. A focal impaired awareness seizure affects a larger part of the hemisphere and the person may lose consciousness.