Population Health and management of epidemics
Hospital-acquired pneumonias (HAPs) are defined as pneumonias occurring ≥48 hours after admission. Discuss the etiological agents in respiratory infections.
Introduction & Definition:
Hospital-acquired pneumonias (HAPs) are defined as pneumonias occurring ≥48 hours after admission. Haps accounts for about 15-20% of HAIs (Hospital acquired infections), and it is reported in 0.6-11% of hospitalized patients.
The risk is high for patients in ICU and among patients undergoing mechanical ventilation has been reported to be high as 30%, so also it is high in patients who are unconscious or have chronic lung disease. Most of the patients who have nosocomial infections are infants, young children, persons more than 65 years of age, persons who have underlying disease, immunosuppression, depressed sensorium or cardiopulmonary disease and persons who have had thoracoabdominal surgery.
Types & Sub-type of Hospital acquired Pneumonias: -There are mainly two types
Fisrt one is Bacterial Pneumonia: -The majority of cases related to various rod-shaped gram-negative organisms (52%), and Staphylococcus aureus (19%), usually of the MRSA type.
Second one is Viral Pneumonia: -Influenza and respiratory syncytial virus and in the immunocompromised host, cytomegalovirus cause 10-20% of infections.
Ventilator associated pneumonia (VAP) is a Sub-Type of hospital-acquired pneumonia(HAP) which occurs in patients who are receiving mechanical ventilation.VAP is defined as pneumonia occurring more than 48 hours after endotracheal intubation and initiation of mechanical ventilation(MV) including pneumonia after extubation .VAP is the frequent ICU acquired infection,occurring in 9-275 of patients intubated for longer than 48 hours.Mechanically-ventilated patients are 6-21 times more likely to develop nosocomial pneumonia than non-ventilated patients,because the endotracheal tube bypasses upper respiratory tract defences ,allowing pooling of oropharyngeal secreations and prevents effective cough.
Etiological agents–
Gram –negative aerobic Bacilli: -The common gram-negative bacilli that cause hospital-acquired pneumonia are Pseudomonas species, Acinetobacter baumannii and Klebsiella pneumoniae followed by E. coli and Staphylococcus aureus, however, the principal infecting organisms vary from one hospital to another depending on resident flora and almost any gram-negative bacillus may be implicated.
A number of studies from India have investigated that Pseudomonas species,Acinetobacter species,Escherichia coli,Klebsiella pneumoniae and Staphylococcus aureus were identified as the common pathogens with varying prevalence.Pseudomonas species and,Acinetobacterspecies,and even Enterobacteriacae are quite often multidrug-resistant due to production of β-lactemases(ESBL), Amp C β-lactemases(MBL).The etiological agents of VAP will vary with different patient populations and types of ICUs.Therefore the local microbial flora needs to be studied in eacg setting to guide more effective rational utilization of antimicrobial agents.
The mortality rate of hospital acquired gram-negative pneumonia is more than 50%, and in spite of treatment may approach 90-100%.
Anaerobic Bacteria: -Respiratory infection due to anaerobic bacteriais usually related to aspiration of oropharyngeal contents, although several cases of secondary hematogenous pneumonia have been reported following pelvic infections.
When aspiration occurs outside the hospital, anaerobic bacteria are almost uniformly present and are the only organisms isolated in more than half of the cases. By contrast, aspiration in the hospital is more likely to contain aerobic bacteria, particularly gram-negative bacilli. However, a mixed infection including aerobes and anaerobes or purely anaerobic aspiration pneumonia is relatively common.
Staphylococcus aureus :- In United states and other Western countries gram-positive organisms especially methicillin –resistant S.aureus plays a mojaor role in HAP nad VAP.Staphylococcus aureus,still cause nosocomial pneumonia.The carrier rate for those organisms is high among both patients and hospital personnel.Infections can therefore be due to patients own strains,or those transmitted to patients by person to person contact.Air-borne transmission of S.aureus is thought to occur only frequently.Mild to moderate pneumonia is usually caused by Methicillin-sensitiveS.aureus,whereas severe HAPs are due to MRSAs.
Other Bacteria: -Virtually every other pathogenic bacterium can be expected to cause pneumonia. However, Streptococcus pneumoniae (Pneumococcus) and meningococcus Streptococccus pyogenes and Haemophillus influenzae are other organisms, which should be considered.
Mycobacterium tuberculosis:-Because of the recent trend towards treating tuberculosis in general hospitals rather than sanatoria,the possibility of spread of this infection in the hospital must be re-evaluated.Usually ,hospitalized patients who are known to have tuberculosis and who are being treated are unlikely to be contagious.By contrast,unsuspected cases of tuberculosis are a potential danger to other patients and hospital personnel alike.Transmision of tuberculosis is by droplet aerosol.
Fungi:-True fungi rarely cause nosocomial infection,because the infective (yeast)form is acquired in nature,whereas the mycelial form,which invades,mammalian tissue is not contagious.Yeast on the other hand,commonly colonize hospitalized patients.Factors predisposing to colonization by Candida species include diabetes mellitus,broad –spectrum antibiotics, or immunosuppresive therapy of any type.Infection of pharynx,trachea and esophagus are relatively common,in contrast,true pulmonary infection due to Candida species is rare. Necrotizing pneumonia due to Aspergillus species is a serious problem usually in immunosuppressed patients and those with widespread malignancy. Infections are usually thought to be endogenous. Other organisms such as Pneumocystitis carinii and Nocardia have on occasion been thought to be hospital acquired.
Viruses: -The problem of hospital acquired viral infections is probably most severe during influenza epidemics. Influenza virus is transmitted by droplets and hospitalized individuals may acquire infection from visitors, other patients, or the medical and nursing staff.Since morbidity and mortality due to influenza is greatest in elderly patients and those who have underlying cardio pulmonary disease,the consequences of this infection are particularly severe in hospitalized patients.
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