Strep Throat (Streptococcal Pharyngitis)

Strep throat or streptococcal pharyngitis is caused by group A Streptococcus bacteria and is the most common bacterial infection of the throat. Although this infection can occur at any age, it is most common in children between the ages of 5 and 15 years. Strep throat is transmitted by person-to-person contact via nasal secretions or saliva (sneezing and/or coughing) by an infected individual or a carrier. On occasion, contaminated food, especially milk and milk products, may be the cause of the infection.

The infection occurs with higher frequency in the late fall, winter, and early spring. Most sore throats are caused by viruses, not by bacteria, and therefore the Centers for Disease Control and Prevention (CDC, Atlanta, GA) recommends that antibiotics not be used unless the test for streptococcal infection proves to be positive, because bacterial resistance to certain antibiotics has been reported. However, if results are positive for Streptococcus, patients should receive antibiotics to minimize transmission and to reduce the risk of further complications, such as rheumatic fever.

Scarlet Fever

Scarlet fever is an upper respiratory disease also caused by an infection with a group A β-hemolytic streptococcus (Streptococcus pyogenes) (Figure 11.2) and once was a serious childhood disease but now is generally treatable. The incubation period is 1 to 2 days and typically begins with a fever and sore throat, but might also exhibit chills, vomiting, abdominal pain, and malaise. The exotoxin produced by the bacteria is responsible for the “strawberry” tongue (Figure 11.3) as well as the characteristic fine rash on the chest, neck, groin, and thighs. The treatment of scarlet fever is the same antibiotic treatment as for strep throat, and complications with appropriate treatment are rare.

Streptococcus pneumoniae

Streptococcus pneumoniae is a gram-positive, encapsulated α-hemolytic diplococcus (Figure 11.4), also known as pneumococcus, and is a common cause of mild respiratory illness, but also a major source of pneumonia. Other than pneumonia the organism is also capable of causing pharyngitis, sinusitis, otitis media, meningitis, osteomyelitis, septic arthritis, endocarditis, peritonitis, pericarditis, cellulitis, and brain abscess. S. pneumoniae is a common inhabitant of the nasopharynx of healthy people, but can be the cause of disease when the organism reaches other areas such as the eustachian tubes, nasal sinuses, and lungs. Furthermore the organism can be found in larger numbers in environments where people spend a lot of time in close proximity and it can be transmitted by person-to-person contact or by inhalation. If the organism is inhaled and not removed by the ciliary escalator (such as in smokers, in whom the cilia have been damaged or degenerated), or the mucous membranes are damaged by a viral infection, the bacteria can attach or even penetrate the mucosa. Once the organism succeeds in getting to a site where it normally is not found it will stimulate the immune system of the host, resulting in the attraction of leukocytes (see Chapter 20, The Immune System). The capsule of S. pneumoniae is resistant to phagocytosis and if immunity is not present the alveolar macrophages are incapable of destroying pneumococci. In this case the bacterium spreads into the bloodstream, where it most likely causes bacteremia. The organism then can get to other areas of the body, causing the conditions mentioned earlier. The virulence of S. pneumoniae is a direct result of its capsule and the encapsulated (smooth) strains are the ones causing disease, whereas the nonencapsulated (rough) strains are avirulent.

The onset of bacterial pneumonia can vary from gradual to sudden. In severe cases patients may have fever, shaking chills, shortness of breath, cough with rust-colored or greenish mucus, and pleuritic chest pain. Fever and sputum production may be absent in elderly persons with pneumococcal pneumonia. Pneumonia can sometimes appear in a mild form, often referred to as “walking pneumonia,” in which symptoms are slight or absent. The risk for bacterial pneumonia is highest for young children, the elderly, people with chronic medical conditions (e.g., heart disease, lung disease, and diabetes), and persons who have a suppressed immune system. Because bacterial pneumonia can easily be passed from one member of the community to another, it can manifest itself in a condition referred to as “community-acquired pneumonia.” This form of the disease occurs worldwide and is a major cause of death among all age groups.

Vaccination is available for the prevention of pneumococcal pneumonia. Two vaccines are currently available: the pneumococcal conjugate vaccine, which is part of the routine infant immunization schedule, and the pneumococcal polysaccharide vaccine used for adult immunization. Vaccination with the pneumococcal polysaccharide vaccine is recommended for all adults age 65 years and older and for persons 2 to 64 years of age with certain chronic illnesses or immunocompromising conditions. Without vaccination the treatment of choice used to be penicillin; however, because of overuse of antibiotics nearly all strains of S. pneumoniae previously susceptible to penicillin show resistance to penicillin as well as to other antibiotics.

Drug-resistant Streptococcus pneumoniae Disease

Drug-resistant Streptococcus pneumoniae disease (DRSP) manifests itself as pneumonia, bacteremia, otitis media, meningitis, peritonitis, and sinusitis. These conditions can be caused by an organism that is resistant to one or more commonly used antibiotics. Overuse of antimicrobial agents is a contributing factor to the emerging resistance and spread of resistant strains. Transmission occurs by person-to-person contact and the risk groups are mostly the elderly, children 2 years of age or older, persons who attend or work at child care centers, immunocompromised patients (e.g., those with AIDS), and also persons who recently used antimicrobial agents. Outbreaks of DRSP have been reported in nursing homes, child care centers, and in institutions for HIV-infected people. A pneumococcal conjugate vaccine is available and its use is preventing many infections due to drug-resistant pneumococci. Future increased use of the vaccine, systematic surveillance, and routine testing for the drug-resistant strains might slow down the emerging drug resistance of this bacterium.

Chlamydial Pneumonia

Chlamydia pneumoniae, now called Chlamydophila pneumoniae, is one of the major causes of pneumonia or bronchitis and is characterized by a gradual onset of cough, with little or no fever. The spectrum of the illness can range from asymptomatic infections to severe disease. Transmissions occur through respiratory secretions of an infected individual and all ages are at risk; however, according to the CDC, it is most common in school-age children. Because the disease is easily passed from one member of the community to another it can give rise to “community-acquired pneumonia.” The infection can be treated with antibiotics and generally the drug of choice is erythromycin.

Pertussis (Whooping Cough)

Pertussis, also known as whooping cough, is a highly contagious disease caused by Bordetella pertussis, an extremely small, aerobic, gram-negative coccobacillus (Figure 11.6). It is a serious disease that can cause permanent disability and even death. Pertussis is easily spread from person to person by airborne droplets discharged from the mucous membranes of infected people. Initial symptoms occur about a week after exposure and resemble those of the common cold. The severe coughing spells start approximately 10 to 12 days later and these spells may lead to vomiting. The coughing often ends with a “whoop” noise caused when the patient is trying to take a breath. Despite the availability of, and high coverage with vaccines, pertussis is one of the leading causes of vaccine-preventable deaths worldwide. Ninety percent of all cases occur in the underdeveloped countries and most deaths involve infants who are either not vaccinated or incompletely vaccinated. Treatment with effective antibiotics, if started early, shortens the infectious period but usually does not alter the outcome of the disease.

Tuberculosis

Tuberculosis (TB) is a deadly infectious disease caused by Mycobacterium tuberculosis (Figure 11.7