Prevalence and Incidence of Flu

Prevalence/Incidence of Flu: Online Medical Books

16 MEDICAL BOOKS ONLINE! Review excerpts from medical books online, free, without registration, for more information about the prevalence and/or incidence of Flu.

Influenza: Causes and incidence
(Professional Guide to Diseases (Eighth Edition))

Transmission of influenza occurs through inhalation of a respiratory droplet from an infected person or by indirect contact with a contaminated object, such as a drinking glass or other items contaminated with respiratory secretions. The influenza virus then invades the epithelium of the respiratory tract, causing inflammation and desquamation.

One of the remarkable features of the influenza virus is its capacity for antigenic variation into numerous distinct strains, allowing it to infect new populations that have little or no immunologic resistance. Antigenic variation is characterized as antigenic drift (minor changes that occur yearly or every few years) and antigenic shift (major changes that lead to pandemics). Influenza viruses are classified into three groups:

❑Type A, the most prevalent, strikes every year, with new serotypes causing epidemics every 3 years.

❑Type B also strikes annually but causes epidemics only every 4 to 6 years.

❑Type C is endemic and causes only sporadic cases.

Each year, tens of millions of people in the United States get the flu; about 114,000 people get sick enough to be hospitalized, and about 36,000 people die.

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Source: Professional Guide to Diseases (Eighth Edition), 2005

Haemophilus influenzae infection: Causes and incidence
(Professional Guide to Diseases (Eighth Edition))

H. influenzae, the cause of this infection, is a small, gram-negative, pleomorphic aerobic bacillus. Transmission occurs by direct contact with secretions or by respiratory droplets. It infects about half of all children before age 1 and virtually all children by age 3, although a haemophilus influenza b vaccine given at ages 2, 4, and 6 months has reduced this number.

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Source: Professional Guide to Diseases (Eighth Edition), 2005

Colorado tick fever: Causes and incidence
(Professional Guide to Diseases (Eighth Edition))

Colorado tick fever is transmitted to humans by a hard-shelled wood tick called Dermacentor andersoni. The adult tick acquires the virus when it bites infected rodents and remains permanently infective.

Incidence is high in Colorado, where up to 15% of people who regularly camp show past exposure. It's much less common in the rest of the United States.

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Source: Professional Guide to Diseases (Eighth Edition), 2005

Lassa fever: Causes and incidence
(Professional Guide to Diseases (Eighth Edition))

A chronic infection in rodents, Lassa virus is transmitted to humans by contact with infected rodent urine, feces, and saliva. The virus enters the bloodstream, lymph vessels, and respiratory and digestive tracts. It then multiplies in the cells of the reticuloendothelial system. In the early stages of this illness, when the virus is in the throat, human transmission may occur through inhalation of infected droplets.

As many as 100 cases of Lassa fever occur annually in western Africa; the disease is rare in the United States.

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Source: Professional Guide to Diseases (Eighth Edition), 2005

Relapsing fever: Causes and incidence
(Professional Guide to Diseases (Eighth Edition))

The body louse (Pediculus humanus corporis) carries louse-borne relapsing fever (B. recurrentis), which typically occurs in epidemics during wars, famines, and mass migrations. Cold weather and crowded living conditions also favor the spread of body lice.

Inoculation takes place when the victim crushes the louse, causing its infected blood or body fluid to soak into the victim's bitten or abraded skin or mucous membranes.

Louse-borne relapsing fever is most common in North and Central Africa, Europe, Asia, and South America. No cases of louse-borne relapsing fever have been reported in the United States since 1900.

Tick-borne relapsing fever, however, is found in the United States and is caused by at least 15 Borrelia species; the three species most commonly identified with tick carriers are B. hermsii (associated with Ornithodoros hermsi), B. turicatae (associated with O. turicata), and B. parkeri (associated with O. parkeri). This form of the disease is most prevalent in Texas and other western states, usually during the summer when ticks and their hosts (chipmunks, goats, squirrels, rabbits, mice, rats, owls, lizards, and prairie dogs) are most active. In the colder weather, outbreaks sometimes afflict people such as campers who sleep in tick-infested cabins.

Because tick bites are virtually painless and most Ornithodoros ticks feed at night but don’t imbed themselves in the victim’s skin, many people are bitten unknowingly.

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Source: Professional Guide to Diseases (Eighth Edition), 2005

Rheumatic fever and rheumatic heart disease: Causes and incidence
(Professional Guide to Diseases (Eighth Edition))

Rheumatic fever appears to be a hypersensitivity reaction to a group A beta-hemolytic streptococcal infection, in which antibodies manufactured to combat streptococci react and produce characteristic lesions at specific tissue sites, especially in the heart and joints. Because very few persons (3%) with streptococcal infections ever contract rheumatic fever, altered host resistance must be involved in its development or recurrence. Although rheumatic fever tends to be familial, this may merely reflect contributing environmental factors. For example, in lower socioeconomic groups, incidence is highest in children between ages 5 and 15, probably as a result of malnutrition and crowded living conditions. This disease strikes generally during cool, damp weather in the winter and early spring. In the United States, it’s most common in the northern states.

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Source: Professional Guide to Diseases (Eighth Edition), 2005

Rocky Mountain spotted fever: Causes and incidence
(Professional Guide to Diseases (Eighth Edition))

R. rickettsii is transmitted to a human or small animal by the prolonged bite (4 to 6 hours) of an adult tick — the wood tick (Dermacentor andersoni) in the west and by the dog tick (Dermacentor variabilis) in the east. Occasionally, it's acquired through inhalation (it can occur in laboratory settings where aerosolization of blood and specimens may occur) or through the contact of abraded skin with tick excreta or tissue juices. (This explains why people should'nt crush ticks between their fingers when removing them from other people and animals.) In most tick-infested areas, 1% to 5% of the ticks harbor R. rickettsii.

Endemic throughout the continental United States, RMSF is particularly prevalent in the southeast and southwest. Because RMSF is associated with outdoor activities, such as camping and backpacking, the incidence of this illness is usually higher in the spring and summer. Epidemiologic surveillance reports for RMSF indicate that the incidence is also higher in children ages 5 to 9, men and boys, and whites.

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Source: Professional Guide to Diseases (Eighth Edition), 2005

Influenza: Influenza - epidemiology
(The 5-Minute Pediatric Consult)

• Although influenza affects people of all ages, the highest morbidity and mortality occur in infants and the geriatric population.
• The attack rate is highest among school-aged children and ranges from 10–40%. 1% of infections result in hospitalization.
• Epidemics of influenza occur almost exclusively during winter months, peak ~2 weeks after the index case, and last 4–8 weeks. Up to 75% of school children in the epidemic region may be affected.
• Transmission of influenza virus occurs by aerosol droplets as well as by direct or indirect contact.
• Complication rates increase in children <2 years old and those with high-risk conditions (see “Complications”).

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Source: The 5-Minute Pediatric Consult, 2008

About prevalence and incidence statistics:

The term 'prevalence' of Flu usually refers to the estimated population of people who are managing Flu at any given time. The term 'incidence' of Flu refers to the annual diagnosis rate, or the number of new cases of Flu diagnosed each year. Hence, these two statistics types can differ: a short-lived disease like flu can have high annual incidence but low prevalence, but a life-long disease like diabetes has a low annual incidence but high prevalence. For more information see about prevalence and incidence statistics.