Streptococcus Pneumoniae: Biology, Epidemiology and Public Health Issues

Pneumococcal Pneumonia

Contents

Overview:

Pneumonia is a serious lung infection that caused by bacteria, viruses and fungi. Pneumonia defined as inflammation of the lung due to infection of total or partial parts of lungs (CDC 2018). In fact, this serious disease affects people of all ages, but the seriousness may increase with people who have lower immunity such as older adults, children and immunocompromised patients HIV/AIDS. According to the Centers for Diseases and Control (CDC), pneumonia is still one of the common causes of death in children aged less than 5 years globally (CDC 2018). In addition, the National Heart, Lung and Blood Institute (NIH),  the danger of pneumonia is increasing with people who are under chemotherapy, organ transplantation and HIV/AIDS, as well as people with the chronic obstructive pulmonary disease ( COPD) (NIH 2018). Pneumonia has many categories; it could be bacterial pneumonia, viral pneumonia, fungal pneumonia, mycoplasma pneumonia, aspiration pneumonia, walking pneumonia (CDC, 2018). This paper is going to explain only one category of lung infection, which caused by bacteria and called Streptococcus Pneumoniae (Pneumococcus).

Section 1: 

Disease Biology

1.1 Disease-Causing Organism, History of Discovery and Surveillance

Pneumococcal pneumonia is an infection of the lung that caused by a gram-positive bacterium called Streptococcus pneumoniae (CDC 2018). Streptococcus pneumonia is a major cause of increased morbidity and mortality worldwide. In 1881, S. pneumonia first isolated by Pasteur from patient’s saliva who had rabies  (CDC 2018).  Streptococcus pneumonia has more than 80 serotypes and the first vaccine in the United States was in 1977 (CDC 2018). However, in 2000, Food and Drug Administration (FDA) has licensed the first 7-valent pneumococcal conjugate vaccine (PCV7) in the U.S. for infants and young children (CDC 2018). The common host of Streptococcus pneumoniae is the human body, in which it does cause pneumonia (Heymann 2015). It also causes acute otitis media infection and sinusitis. According to Heymann, streptococcus has two groups; group A streptococci and group B streptococci (Heymann, 2015).  They differ in the route of transmission. The route by which group A streptococci is spread is by aerosol droplets from human to human and fomites (Heymann 2015).  While group B streptococcus is commonly residing in the normal vaginal flora and when the mother is infected with the organism, the infant could get the organisms during delivery or invasive during pregnancy (Stevens and Kaplan, 2000). According to Birgitta et al, the life cycle of bacterial pneumonia starts with respiratory tract mucosal infection and it can spread to cause more serious problems such as septicemia and meningitis (Birgitta et al 2013). About 20% of people with pneumonia in the United States get septicemia and 5% die from pneumococcal pneumonia (Birgitta et al 2013).

Despite the fact that pneumococcal pneumonia is a lethal disease, it can be also colonized in the nasopharynx without causing any symptoms (S. Nunes et al 2005). Many of those who are colonized with the organism may develop resistance to the treatment of streptococcus pneumonia. A yearly surveillance of nasopharyngeal carriers of pneumococci in 1996  on children done by S. Nunes et al shows that most of these children have developed drug resistance during asymptomatic S. pneumonia colonization phase; and once the normal flora weakens, they get symptoms of pneumonia (S. Nunes et al 2005). The CDC PINK BOOK illustrates that the estimated hospitalization in the united states is about 400,000 per year (CDC 2018). Also, pneumococcal pneumonia could present as a primary disease or as secondary disease following the common cold. According to the CDC,  pneumococcal pneumonia infection occurs as a common complication of influenza during the influenza season among children and elderly who did not get the influenza vaccine(CDC 2018). The recent statistics of case fatality rate among elderly done by the CDC surveillance estimates that nearly 20% – 60 % of CFR in the United States (CDC 2018).  

                   Figure (1-1):  This figure illustrates the difference between the appearance of

                   healthy air sac and the air sac of infected person with streptococcus pneumonia.

1.2 Host Defense System

 Innate immune responses have a vital role in host defense against the streptococcus pneumonia, especially at the earliest stages of the infection (Lumin Zhang 2015). When the S. pneumonia entire the nasopharynx and migrate to the alveoli,  S. pneumonia activates the phagocytic cells and the lung also will produce mucus, which lead to a productive cough with fever (CDC 2018). Figure (1-1) illustrates the difference between healthy air sac and infected air sac; it shows also that the alveoli are full of mucus in comparing with the clear alveoli. Then, the bacteria adhere to the alveolar epithelium and replicate, which lead to activate B cell to produce antibodies (Lumin Zhang 2015). With the low immunity especially for HIV patients and patients under chemotherapy,  the S. pneumonia will cause severe damage to the alveoli causing invasive pneumonia to the blood and other parts of the body (Lumin Zhang 2015).

1.3 Disease Types and Presentation Symptoms and Risk factors

        Pneumococcal pneumonia has a short incubation period from one to three days (CDC 2018). The most common clinical presentation of the pneumococcal disease is fever, chills, chest pain, productive cough, dyspnea, hypoxia and weakness (Heymann 2015). There are two types for the disease; Community-acquired pneumonia for people who develop symptoms out of the hospital and Hospital-acquired infection for people who get the disease during their hospitalization (Scott 2007). According to CDC community-acquired pneumonia cases are about  36% higher in adults compared with the hospital-acquired infection (CDC 2018). The risk of severe clinical symptoms is increasing with children, older adults and immune compromised patients. Those group of people is usually experiencing what called invasive pneumonia (CDC 2018). Figure (1-2) shows the life cycle of the organism and the possible complications of streptococcus pneumonia and how the organism can be transmitted. Invasive pneumonia means that the streptococcus pneumonia germs invade the body parts through lung, infection, otitis infection or ear infection (Heymann 2015). For example, the germs of S. pneumonia can invade the bloodstream, tissues and cerebrospinal fluid after severe destructions in the air sac(CSF). Therefore, pneumococcal pneumonia has many other complications such as pericarditis (infection of the heart muscle), bacteremia (bloodstream infection) and meningitis (infection of the brain cover) (Heymann, 2015).

                  Figure (1-2):  This figure shows the life cycle of Streptococcus

                 Pneumoniae and the pathogenesis of pneumococcal disease.

1.4 Disease Diagnosis Methods

Diagnosing patients with streptococcus pneumonia sometimes is hard due to the similar clinical symptoms with other diseases. Without the microbiological results, most of the patients present with a sore throat, which makes the disease difficult to diagnose clinically (Giesecke, J., 2017). To diagnose patients with S .pneumonia, the patient may go through the following tests: chest x-ray, blood culture, sputum culture, urine culture and chest CT scan (NIH, 2018). Urine culture is usually common when the patient has a very serious infection of streptococcus pneumonia (CDC, 2018). Furthermore,  Heymann illustrates in his book that the blood culturing method is a definitive way to diagnose S. pneumonia and helps to identify the gram stain type (Heymann, 2015). The chest x-ray could also help in identifying the type of pneumonia wither upper lobes or lower lobes of the lung (Heymann, 2015).  CDC also introduces a quick way to test for the disease by checking the antigen of the streptococcus pneumonia (CDC 2018).  Also, a recommendation produced by the Infectious Diseases Society of America/American Thoracic Society (IDSA/ATS) suggested that the sputum specimens should be collected before the start of antibiotic treatment in inpatients (Watkins and  Lemonovich, 2011). Moreover, the precipitin test is a sensitive serological method that can detect both of group A or B antigens (Stevens and Kaplan, 2000). Moreover,  An interesting study done by Nakar, S et al, explains another method of knowing if the patient is infected with streptococcus pneumonia (Nakar, S et al, 1994). This study shows that most of the patients who present symptoms of a sore throat and their mouth smells putrid, they usually get positive cultures of the streptococcus organisms (Nakar, S et al, 1994). All these methods would help in diagnosing the patients better, as well as determining the type of streptococcus withers A streptococci or B streptococci.

1.5 Streptococcus Treatment and Control

         Streptococcus pneumonia can be treated by using the Beta-lactam antibiotics such as Penicillin for all ages (CDC, 2018).  The CDC recommended also to use the Amoxicillin antibiotic as a first choice in children less than five years (CDC, 2018). Many patients who are colonized with the disease develop antibiotics resistance to the Beta-lactam group (CDC, 2018). Therefore, with the increase in the prevalence of antibiotic resistance, CDC has recommended using alternatives such as co-amoxiclav, azithromycin and clarithromycin (CDC, 2018).  Moreover, alternative can be used with patients who are allergic to the Beta-lactam antibiotics. The administration route for antibiotics depends on the patients status. It can be administered orally for conscious patients and intravenously for patients who are experiencing severe illness, such as meningitis and altered of consciousness (Heymann, 2015).  In addition to the antibiotics, patients also need a supportive care such as oxygen, which will improve the status of the patient (Watkins and  Lemonovich, 2011). The patient may also need to take a broad-spectrum antibiotic or long-acting benzathine penicillin as a secondary prevention of possible complication (Heymann, 2015). According to Heymann, most of the patients who have treated my experience reinfection, especially after valve surgery. Therefore, life-long prophylaxis is recommended. 

 Streptococcus pneumonia can be prevented by vaccination. There are two common types of S. pneumonia vaccines that recommended by CDC. The first recommended vaccine called 23-valent Pneumococcal Polysaccharides Vaccine (PPV23) (CDC, 2018). This vaccine covers about 23 serotypes of streptococcus pneumonia.  The second suggested the vaccine is  7-valent Pneumococcal Conjugate Vaccine (PCV7) (CDC, 2018). This PCV7 is a newer type and covers more 7 serotypes of streptococcus pneumonia. However, in 2010,  a pneumococcal conjugate vaccine has updated to cover more six serotypes and has become with a new name called (PCV 13). All these types of vaccines are in the form of inactivated vaccine (killed vaccine), which will not cause the disease if they are introduced to people who are with low immunity. Center of Disease and Control suggests that children less than 5 years old and adults more than 65 years old have to get the vaccine. Figure (1-3) illustrates the recommended type of vaccine by ages. Furthermore, people who are immunocompromised due to HIV, chemotherapy or have done splenectomy have to take the vaccine as well (CDC, 2018).  Figure (1-4) shows the recommended type of vaccine by health. condition. In fact, the influenza vaccine may decrease the risk of S. pneumonia in elderly by 50% (Ortqvist. A et al, 2005). Finally, all these guidelines from CDC help in the prevention and controlling pneumococcal pneumonia worldwide. 

           Figure (1-3): This graph shows the recommended immunization for adult by age.

           The part surrounded by red square is for pneumococcal pneumonia. The vaccine

           is highly recommended by CDC for people over 65 years old.

         Figure (1-4): This graph shows the recommended immunization for adult by Health 

         condition. The part surrounded by red square is for pneumococcal pneumonia. The 

         PCV13 is highly recommended by CDC for people with weak immunity, HIV, Kidney

         disease and spleen removed. While PSV23 is suggested  for all previous health

         conditions in addition to people with heart disease, chronic pulmonary disease ,

         diabetes and chronic liver disease.

Section 2:

Disease Epidemiology

2.1 The major modes of transmission

Streptococcus pneumonia can be transmitted by both respiratory droplets and fomites (CDC, 2018). The incidence of S. pneumonia both types A and B  rise in childhood (Patterson, M. J., 1996). The human is the main reservoir of the S. Pneumonia organisms and does not have a zoonotic reservoir. (Heymann, 2018).  Normally the S. pneumonia organism colonizes in the nasopharynx (Weber & Rutala, 2003).  During winter, the rate of disease colonization is increased due to the increase in the prevalence of seasonal influenza (Weber & Rutala, 2003).  Living in crowded facilities such as prisons, military camps and shelters have shown an increase in the epidemic of  S. pneumonia due to person to person direct contact and shared personal equipment (Heymann, 2015).  Figure (2-1) shows the incidence of invasive S. pneumonia. The infectivity is increased in the age group less than five years old, as well as older adults. However, the mortality shows higher in the older adult comparing the lower age groups in figure (2-2) (Weber & Rutala, 2003).  

Figure (2-1): The infection rate by age                                Figure (2-2): The case fatality rate by age

2.2 Pneumococcal Pneumonia Case Definition

       According to the Center of Disease and Control, invasive pneumococcal pneumonia can be defined clinically depending on the site of infection such as sepsis, and meningitis (CDC, 2018).  However, to confirm that the patient is infected with S. pneumonia, laboratory identification is important (CDC, 2018).  Furthermore, health event can be reported if the second specimen shows a positive finding of S. pneumonia after thirty days from the first specimen (CDC, 2018). Indeed, CDC has classified the cases to probable and confirmed.  The probable case is when patient match supportive laboratory evidence (CDC, 2018). Supportive laboratory evidence means that there is consistent laboratory finding with the diagnosis, but it is not meeting the criteria of confirmation (Case Definitions, A. L., 1990). Case definition helps the epidemiologists to recognize the disease during outbreaks , as well as it facilitates the reporting systems of disease incidence.

2.3 Pneumococcal Pneumonia  Worldwide Distribution  and Trends

      Streptococcus pneumonia is a major interest for public health experts to assess its distribution. The incidence of the disease may increase in countries with low income, poor sanitation systems and poor nutrition (WHO, 2018). Figure (2-3) illustrates the global distribution of S. Pneumonia incidence for children. 44% of the disease incidence was for children who are less than five years in India, China, Pakistan, Bangladesh, Indonesia and Nigeria (WHO, 2018).

The global distribution helps the public health departments to increase awareness and vaccinations in these high prevalent countries.

         Figure (2-3): this graph shows the global distribution of the incidence of childhood

         S. pneumonia at country level. The. Darker areas are the countries that are prevalent

          with the disease. 

Furthermore, the trend of the disease is important in terms of understanding and improving public health prevention standers, as well as treatment methods. Figure (2-4) shows the trend of invasive pneumonia for children under five years and the time and type of vaccine introduced from 1998 to 2015 (CDC, 2018).  The trend appears to decrease dramatically 45 % after vaccines introduction (CDC, 2018). This graph helps public health practitioners to recognize the best way of disease prevention and control globally. Moreover, it facilitates the pharmacologists to recognize if they need to add more serotypes for better controlling, as well as increasing the quality of vaccines.

                                                                                    Figure (2-4): The trend invasive 

                                                                                                         S. pneumonia for Children < 5 Years

Section 3: Public Health Aspects of Pneumococcal Pneumonia

3.1 Public Health Practices

Even though S. pneumonia has many types of vaccines, S. pneumonia continuous to cause morbidity and mortality globally.  More than one million patients died due to an invasive S. pneumonia globally (Walsh & Camilli 2011).  In the United States, about 7 millions of otitis media caused by S. pneumonia infection. Center of Diseases and Control is the best in obtaining the latest update about S. Pneumonia, as well as the global trends. Creating obligatory reporting systems are important to understand the epidemic of S. Pneumonia disease (Heymann, 2015).

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Epidemiologists have to determine the source of the disease in order to understand the pattern of S. pneumonia outbreaks, as well as applying the best methods of prevention and control. Moreover, recognizing the infected mother with S. pneumonia is critical. Health care providers could save the neonate from the infection by performing a cesarean section to avoid direct contact with the vaginal secretions during delivery (Heymann, 2015). Also, applying the CDC recommendations of taking the vaccine could help in reducing the incidence of S. Pneumonia. It is also highly suggested to increase the awareness about influenza vaccines since the S. pneumonia could occur due to secondary infection (Weinberger, 2014). Figure (3-1) shows the trend of influenza associated with the increase in the incidence of invasive S. pneumonia.

                                    Figure (3-1): This figure illustrates the effect of influenza on the

                                   incidence on invasive pneumonia by age groups. Number of cases

                                    are relatively high for age group (0-14) with very wide confidence

                                     interval.

3.2 Public Health Impact

  One of the major issues with S. pneumonia is drug resistance. Patients who are colonized usually are asymptomatic (NIH, 2018). Therefore, many patients develop drug resistance during the colonization phase (Heymann, 2015).  This is would increase the burden of S. pneumonia globally. Also, it would alter the public health practices and efforts of disease controlling and prevention because colonized patients would transfer the organisms to others (Heyman, 2015). S. pneumonia vaccination is the most effective way of controlling the disease and decreasing the transmission between colonized people as well. According to  Hu et al.,  using PCV7 vaccine universally as a policy among infant would have a huge positive impact on decreasing morbidity and mortality among infants (Hu et al, 2014).  Overall, applying the CDC recommendations and increasing the awareness about the influenza vaccines would have a substantial impact on public health.

Section 4: References

References

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Figures:

• Cover Page Pic: https://www.nationaljewish.org/health-insights/health-tips/is-my-cough-pneumonia
• Figure (1-1): https://www.medindia.net/patients/patientinfo/pneumonia.htm
• Figure (1-2) :  https://www.nature.com/articles/s41579-018-0001-8/figures/1
• Figure (1-3): https://www.cdc.gov/vaccines/schedules/downloads/adult/adult-schedule-easy-read.pdf
• Figure (1-4): https://www.cdc.gov/vaccines/schedules/downloads/adult/adult-schedule-easy-read.pdf
• Figure (2-1): https://www.medscape.org/viewarticle/451448_3
• Figure (2-2): https://www.medscape.org/viewarticle/451448_3
• Figure (2-3): http://www.who.int/bulletin/volumes/86/5/07-048769/en/
• Figure (2-4): https://www.cdc.gov/vaccines/pubs/surv-manual/chpt11-pneumo.html
• Figure (3-1): http://erj.ersjournals.com/content/43/3/833