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Classification
Respiratory
symptoms of pneumonia include an acute cough, which can either be nonproductive
or productive of purulent or rust-colored sputum, and at least one abnormal chest
finding (eg diminished breath sounds, rhonchi, crackles, or wheeze). Systemic
symptoms may also occur which include pleuritic chest pain, chills or rigors, and
confusion. Abnormal vital signs that prompt suspicion include a respiratory
rate of >20 breaths/minute, heart rate of >100 beats/minute, and fever
>37.8°C. Chest X-ray findings may show lobar consolidation, bilateral
infiltrates, or cavitation. It is potentially life-threatening, especially in older
adults and those with comorbid disease.


Low-risk Community-acquired Pneumonia (CAP)
Patients classified under low-risk community-acquired pneumonia do not have any alteration in mental status, have no suspicion of possible aspiration, do not have any comorbid condition, or have stable comorbid condition(s). Chest X-ray findings may show localized infiltrates but without pleural effusion.
They also typically present with the following vital signs:
- Respiratory rate of <30 breaths/minute
- Heart rate of <125 beats/minute
- Temperature of >36°C or <40°C
- Systolic blood pressure of >90 mmHg
- Diastolic blood pressure >60 mmHg
Moderate-risk
Community-acquired Pneumonia (CAP)
Patients classified under moderate-risk
community-acquired pneumonia may have an acute onset of altered mental state,
suspected aspiration, extrapulmonary evidence of sepsis (eg endocarditis,
arthritis, encephalitis, otitis media), or an unstable comorbid condition (eg uncontrolled
diabetes mellitus, active malignancies, congestive heart failure class II-IV, chronic
obstructive pulmonary disease in acute exacerbation, decompensated liver
disease). Chest X-ray findings may show bilateral or multilobar involvement, progression
of the lesion to 50% of initial finding within 24 hours, pleural effusion, or
abscess.
They also typically
present with the following vital signs:
- Respiratory rate of ≥30 breaths/minute
- Heart rate of ≥125 beats/minute
- Temperature of ≤36°C or ≥40°C
- Systolic blood pressure of <90 mmHg
- Diastolic blood pressure of ≤60 mmHg
High-risk
Community-acquired Pneumonia (CAP)
Clinical
Features
Patients classified under high-risk
community-acquired pneumonia exhibit either one major criterion or ≥3 minor
criteria.
The minor criteria are as follows:
- Respiratory rate of ≥30 breaths/minute
- Arterial oxygen partial pressure/Fractional inspired oxygen (PaO2/FiO2) ratio of ≤250 mmHg
- Multilobar infiltrates
- Confusion or disorientation
- Blood urea nitrogen (BUN) of ≥20 mg/dL
- White blood cell count (WBC) <4000 cells/μL
- Platelet count <100,000/μL
- Core temperature <36°C
- Hypotension needing aggressive fluid resuscitation
The major criteria are as follows:
- Septic shock needing vasopressors
- Respiratory failure needing mechanical ventilation
Introduction
Pneumonia is an acute infection of the pulmonary parenchyma accompanied by symptoms of acute illness and abnormal chest findings. It commonly presents with at least one abnormal chest finding of diminished breath sounds, rhonchi, crackles, or wheezing, and X-ray may show lobar consolidation, bilateral infiltrates, or cavitation. It occurs in the very young and the very old. It is a potentially life-threatening disease, especially in older adults and those with comorbid illnesses.
Epidemiology
ปอดบวมยังคงเป็นสาเหตุหลักของการเสียชีวิตจากโรคติดเชื้อทั้งในผู้ใหญ่และเด็กอายุต่ำกว่า 5 ปี อัตรานี้สูงกว่าในเด็กเล็ก (เด็กอายุต่ำกว่า 5 ปี) และผู้สูงอายุ (ผู้ใหญ่ที่มีอายุมากกว่า 60 ปี) มันพบได้บ่อยในผู้ชายมากกว่าผู้หญิง อินเดียมีสัดส่วนของภาระโรคปอดบวมถึง 23% ของทั่วโลกและมีอัตราการเสียชีวิตจากโรคนี้อยู่ที่ 14-30% ในประเทศจีน อัตราการแพร่ระบาดในช่วงสองสัปดาห์อยู่ที่ 0.9% ในปี 2003 และ 1.1% ในปี 2008 การศึกษาที่เกาหลีใต้รายงานว่าอัตราการเข้ารักษาในโรงพยาบาลอยู่ที่ 520 ต่อประชากร 100,000 คนในปี 2002-2005 ซึ่งสูงที่สุดในกลุ่มอายุ ≥75 ปี ในชนบทของประเทศไทย อัตราการเข้ารับการรักษาในโรงพยาบาลที่ประมาณการไว้มีค่าตั้งแต่ 177-580 ต่อประชากร 100,000 คนในปี 2002-2003 และ 199-256 ต่อประชากร 100,000 คนในปี 2006 ตามการศึกษาทางระบาดวิทยา ในฟิลิปปินส์ โรคปอดบวมเป็นหนึ่งในข้อเรียกร้องทางการแพทย์ที่ได้รับการชดเชยสูงสุดผ่านผู้ให้บริการประกันภัยรายใหญ่ที่สุด ทำให้เป็นปัญหาสุขภาพที่สำคัญในประเทศ มันเป็นสาเหตุหลักอันดับที่หกของการเจ็บป่วยและการเสียชีวิต ในภูมิภาคเอเชียแปซิฟิก อัตราการเสียชีวิตประมาณ 1.1-30% โดยญี่ปุ่น อินเดีย ฟิลิปปินส์ ปากีสถาน มาเลเซีย และกัมพูชามีอัตราการเสียชีวิตสูงที่สุด อัตราการเสียชีวิตสูงกว่าในผู้ป่วยที่ต้องเข้ารับการรักษาในโรงพยาบาล ผู้ที่มีโรคประจำตัว ผู้ที่มาจากประเทศที่มีรายได้น้อย ผู้ที่อาศัยอยู่ในบ้านพักคนชรา หรือผู้สูงอายุ
Etiology
The development of community-acquired pneumonia may
be due to microaspiration, presence of a defect in the host defenses, possible
exposure to a virulent microorganism, or due to presence of an overwhelming
inoculum. Microaspiration is a mechanism by which the constituents of both the
microbiota and pathogens reach the lungs. Other mechanisms by which a pathogen gains
access to the lungs are via hematogenous spread, contiguous spread, and
macroaspiration.
The following are the virulence factors of some
causative agents of community-acquired pneumonia:
- Chlamydia pneumoniae possesses ciliostatic factor
- Mycoplasma pneumoniae shears off the cilia
- Influenza virus causes a marked reduction in the tracheal mucus velocity for up to 12 weeks post-infection
- Streptococcus pneumoniae and Neisseria meningitides produce proteases and split secretory IgA; other virulence factors include inhibition of phagocytosis, pneumolysin, and thiol-activated cytolysin
- Mycobacterium sp, Nocardia sp, and Legionella sp are all resistant to microbicidal activity (phagocytes)
Pathophysiology
- Administration of immunosuppressive agents (eg recipients of solid organ or stem cell transplants or those receiving chemotherapy, and long-term steroids)
- Comorbid conditions:
- Chronic respiratory disease (eg bronchial asthma, chronic bronchitis, cystic fibrosis, bronchiectasis, chronic obstructive pulmonary disease, pulmonary edema)
- Genetic disorder (eg Kartagener's syndrome)
- Influenza
- Chronic renal disorders
- Hepatic conditions
- Diabetes mellitus
- Malignancy (eg myeloma, lung cancer)
- Immunocompromised states such as human immunodeficiency virus (HIV) infection, hypogammaglobulinemia (IgG2 immunodeficiency), hyperimmunoglobulin E (Job) syndrome, surgical asplenia, or sickle cell disease
- Continual contact with children (eg young children attending childcare, preschool teachers)
- Cigarette smoking and alcoholism
- Elderly (>65 years old)
- Immunosuppression and malnutrition
- Medications (eg inhaled corticosteroids, proton pump inhibitors and H2 blockers, antipsychotic drugs, and sedatives)
- Oxygen and inhalation therapy particularly containing steroids or using plastic spacers
- Other risk factors for young adults include training in the military and presence of low cholesterol or albumin levels
- People who are homeless and overcrowding inside jails and human shelters
Risk Factors
Community-acquired
pneumonia may be classified as low-, moderate-, or high-risk depending on the
patient’s overall clinical status, vital signs, presence of co-morbidities, and
chest X-ray findings.
Low-risk
Community-acquired Pneumonia (CAP)
Low-risk
community-acquired pneumonia is associated with low morbidity and mortality
rate of <5% and is therefore suitable for outpatient care. Patients considered
at low-risk community-acquired pneumonia are those with stable vital signs and stable
comorbid conditions (eg controlled diabetes mellitus [DM], coronary artery
disease [CAD], renal insufficiency, COPD,
chronic liver disease, chronic alcohol abuse, and asplenia).
They may be treated as
outpatients with a reasonable assurance of follow-up and sufficient social
support. Hospitalization of patients with low-risk community-acquired pneumonia
may be required if there are complications of pneumonia itself, exacerbation of
underlying diseases, advanced age (≥65 years of age), inability to reliably take oral medications or receive
outpatient care, inability to maintain oral intake, uncontrollable vomiting,
cognitive dysfunction, and social problems (eg unavailability of a caregiver,
homelessness).
The possible pathogens include Streptococcus
pneumoniae, Haemophilus influenzae, Chlamydophila pneumoniae, Mycoplasma
pneumoniae, Moraxella catarrhalis, and enteric Gram-negative bacilli (among
those with comorbid illnesses).
Moderate-risk
Community-acquired Pneumonia (CAP)
Moderate-risk
community-acquired pneumonia is associated with a
complicated outcome and higher mortality rate, thus in-hospital parenteral
therapy is recommended. In patients with prior respiratory tract
colonization, culture, swab, or polymerase chain reaction (PCR) tests must be
taken prior to starting empiric therapy.
The possible pathogens
include Streptococcus pneumoniae, Haemophilus influenzae, Chlamydophila
pneumoniae, Mycoplasma pneumoniae, Moraxella catarrhalis, enteric
Gram-negative bacilli, Legionella pneumophila, and anaerobes (in
patients with risk of aspiration).
High-risk
Community-acquired Pneumonia (CAP)
High-risk
community-acquired pneumonia is associated with a mortality rate of 36%, thus it
is managed in a hospital setting and those with hemodynamic instability or
respiratory failure should be admitted to the intensive care unit (ICU).
The possible pathogens
include Streptococcus pneumoniae, Haemophilus influenzae, Chlamydophila
pneumoniae, Mycoplasma pneumoniae, Moraxella catarrhalis, enteric
Gram-negative bacilli, Legionella pneumophila, Staphylococcus aureus, Pseudomonas
aeruginosa, Pneumocystis jirovecii, Klebsiella pneumoniae, Acinetobacter
sp, and anaerobes (in patients with risk of aspiration).
Patients who have a history of chronic (>7 days within the past
month) use of broad-spectrum antibiotic therapy, bronchiectasis, malnutrition,
and on steroid therapy are at risk of developing Pseudomonas aeruginosa infection.