DR.T.V.RAO MD 1

Dr.T.V.Rao MD

LOWER RESPIRATORY BACTERIAL INFECTIONS

AETIOLOGY, DIAGNOSIS

DR.T.V.RAO MD 2

RESPIRATORY SYSTEM ENVIRONMENT IS DIVERSE

• Upper respiratory system

• Nose, pharynx, associated structures

• Purpose: to take in, warm and moisten air

• Most common site of infections

• Lower respiratory system

• Larynx, trachea, bronchi, alveoli

• Purpose: ventilation, gas exchange

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ANATOMY OF THE RESPIRATORY SYSTEM (AND SITES OF INFECTION)

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CLINICAL PRESENTATION: LOWER RESPIRATORY TRACT INFECTION

• Acute Infection:• Fever, chills

• Back pain, myalgias, arthralgias

• Headache, malaise, chills

• Nausea, vomiting

• Chest Infection:• Cough

• Chest pain

• Rales, wheezing, noisy chest

• Characteristic changes on chest x-rays

• Increasing respiratory distress, may require mechanical ventilation

LOWER RESPIRATORY TRACT INFECTIONSEPIDEMIOLOGY

• Pneumonia is the sixth leading cause of death in US

• Increasing numbers of patients at risk• Aging population

• Increase in patients with immunocompromising conditions

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DIAGNOSIS DEPENDS ON CLINICAL PRESENTATION AND AGE TOO

• Most of these cases diagnosis depends on clinical presentation and minimum laboratory and radiologic investigations may be needed most of these cases recovered smoothly with appropriate management unless an underlying lung pathological or systemic disease may worsen the condition or continue with chronicity appropriate follow-up of these patients in OPC is appreciated especially after discharge from hospital

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• Infections of the lower respiratory tract are the leading cause of cause of mortality world wide. Streptococcus pneumoniae is the leading bacterial agent of community acquired pneumonia along with Haemophilus influenza and Moraxella catarrhalis

LOWER RESPIRATORY TRACT

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Pneumococcus is the most common bacterial pathogen causing febrile pneumonia in children and adults

The clinical syndrome is characteristic and distinctive : acute onset of high, spiking fever, with chills, cough, and sputum production

PNEUMOCOCCUS A SIGNIFICANT PATHOGEN

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• Acute bronchitis• Community acquired

pneumonia• Hospital acquired

pneumonia• Pneumonia in the

immunocompromised host

CATEGORIES OF LOWER RESPIRATORY TRACT INFECTIONS

COMMUNITY ACQUIRED PNEUMONIAETIOLOGIC AGENTS

Pathogen Frequency (%)Streptococcus pneumoniae 66

Haemophilus influenza 1-12

M catarrhalis 10

Legionella species 2-15

Mycoplasma pneumoniae 2-14

Klebsiella species 3-14

Enteric gram negative bacilli 6-9

Staphylococcus aureus 3-14

Chlamydia species 5-15

Influenza viruses 5-12

Other viruses <1-12

Unknown 23-49

Carroll KC. 2002. J Clin Microbiol 40:3115-3120. Sharp SE, et.al. Cumitech 2003DR.T.V.RAO MD 10

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SPECIMEN COLLECTION:

The patient should be standing, If possible or sitting upright in bed.He or she should take deep breath to full the lungs, and empty then in one breath, coughing as hard and as deeply as possible.Sputum brought up should be spit into screw capped container.Visually inspect the specimen.Tighten the cap of the container and send immediately to lab.

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• Sputum of less than 2ml should not be processed unless obviously purulent

• Only 1 sputum per 24hr .submitted

• Some scoring system should be used to reject specimen that re oral contamination.

SPUTUM COLLECTION

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TRANSPORTATION OF SPUTUM

• Transportation in <2 hr is recommended with refrigeration if delays anticipated.

• Handle all samples using universal precautions.

• Perform Gram stain and plant specimen as soon as possible

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INDUCED SPUTUM Patients who are unable to produce sputum may be

assisted by respiratory therapy technician. Aerosol induced specimen are collected by allowing the patient to breath aerosolized droplets of a solution of 15% sodium chloride and 10% glycerin for approximately 10 minute obtaining such specimen may avoid the need for a more invasive procedures ,such as bronchoscopy or needle aspiration, in many cases.

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BRONCHOALVEOLAR LAVAGE (BAL) SPECIMEN ACCEPTABILITY

• Microscopic examination of Gram-stained smear

• Acceptable

• <1% of cells present are squamous epithelial cells

• Unacceptable

• >1% of cells present are squamous epithelial cells

Thorpe JE et. al. 1987. Bronchoalveolar lavage for diagnosing acute bacterial pneumonia. J. Infect. Dis. 155:855-861

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METHODS OF COLLECTION IS IMPORTANT..

• Sputum collected under supervision of nurse or resident• Samples were processed immediately

• Screened for epithelial cells

• Screened for predominant morphotype (> 75% of the organisms seen)

• Sputum planted to blood agar, chocolate agar and MacConkey agar

• Strictly defined clinical and diagnostic parameters

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• Prepare a gram stain smear for all lower respiratory tract specimens to determine the presence of oropharyngeal contamination (indicated by squamous epithelial cells) and lower respiratory tract secretions (indicated by WBCs) as well as to identity the most likely pathogens (Indicated by the predominant organisms associated with WBCs).

MICROSCOPIC EXAMINATION

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SPUTUM GRAM STAIN

Good quality specimens

• Quantify number and types of inflammatory cells

• Note presence of bronchial epithelial cells

• Concentrate on areas with WBCs when looking for organisms

• Determine if there is a predominant organism (> 10 per oil immersion field)• Semiquantitate and report organism with descriptive

• If no predominant organism is present, report “mixed gram positive and gram negative flora”

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SPUTUM GRAM STAIN IS HELPFUL - YES

Proponents

• Demonstration of predominant morphotype on Gram stain guides therapy

• Accuracy is good when strict criteria are used

• Cheap, so why not?

Antagonists• Poor specimen collection• Intralaboratory variability

(Gram stain interpretation)• Low sensitivity and

specificity• Empiric treatment

guidelines• Do much dependence ???

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STUDIES PROVE ...• Overall sensitivity and specificity for pneumococcal

pneumonia: 57% and 97%

• Overall sensitivity and specificity for H. influenza pneumonia: 82 % and 99%

• Gram stain gave presumptive diagnosis in 80% of patients who had a good specimen submitted

• > 95% of patients in whom a predominant morphotype was seen on Gram stain received monotherapy

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REPORT GRAM STAINING WITH CAUTION

• Be as descriptive as possible

• Moderate neutrophils

• Moderate Gram positive diplococcic suggestive of Streptococcus pneumoniae

• Few bacteria suggestive of oral flora

• Keep report short—avoid line listing of all morphotypes present

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• If no squamous epithelial cell are found, report “ No epithelial cells seen”

• If only a few epithelial cells are found report “ Few epithelial cells seen”

• If abundant epithelial cells seen, indicating oropharyngeal contamination, such specimens are graded as unsatisfactory sample.

•

SQUAMOUS EPITHELIAL CELLS

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• If no WBC are found report “No WBCs seen”

• If WBCs are present in any amount state as few, moderate or numerous WBCs seen.

REPORTING THE PRESENCE OF LEUCOCYTES:

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INTERPRETATION OF GRAM STAIN:

• None Few Moderate Numerous

Squamous epithelial cells/ LPF* 0 1-9 10-24 >25

• Neutrophils/LPF* 0 1-9 10-24 >25

•

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GRAM STAINING – REPORTING MICROBIAL OBSERVATIONS

• Type / Number of organisms / HPF**• Gram-positive cocci

• Gram-negative cocci

• Gram-negative rods

• Gram-positive rods

• PF*: (low power field) x 10 (examine 10-20 fields)

• HPF**: (high power field) oil immersion

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PROCESSING SPECIMENS FOR CULTURE

• Process specimens in biological safety cabinet, as aerosol can result in laboratory-squired respiratory infections.

• Process all specimens as rapidly as possible, especially specimen from emergency department, and inpatients. Select the most purulent or most blood-tinged portion of the specimen. Significant growth above the cutoff should be reported; however if more than one pathogen is isolated than it is suggestive of oropharyngeal contamination and clinical correlation should be done before reporting the samples.

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• Sheep Blood Agar

• MacConkey agar

• Chocolate agar

CHOOSING CULTURE MEDIA:

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• Most of the commonly sought etiologic agents of lower respiratory tract infection will isolated on routinely used media : 5% sheep blood agar ,MacConkey agar for isolation and differentiation of gram-negative bacilli ,and chocolate agar for Neisseria spp and Haemophilus .

ROUTINE CULTURE

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CONTAMINATION WITH ORAL FLORA INTERFERES RESULTS

• Because of contaminating oral flora ,sputum specimens, specimens obtained by bronchial washing, and lavage tracheostomy, or endotracheal tube aspirates are not inoculated to enriched broth or incubated anaerobically. Only specimens obtained by percutaneous aspiration (including trans tracheal aspiration )and by protected bronchial brush are suitable for anaerobic culture: he latter must be done quantitatively for proper interpretation.

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CULTURING SPECIMENS FROM CYSTIC FIBROSIS

• Sputum specimens from patients known to have cystic fibrosis should be inoculated to selective agar ,such as manitol salt agar for recovery of S .aureus and selective horse blood-bacitracin ,incubated anaerobically and aerobically ,for recovery of H,influenzae that may be obscured by the mucoid P,aeroginosa on routine media.

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SPUTUM AND ENDOTRACHEAL SUCTIONCULTURE EVALUATION

• Identify and perform susceptibility testing on 2-3 potential pathogens seen as predominant on Gram stain

• Alpha strep—rule out S. pneumoniae

• Yeast—rule out Cryptococcus neoformans only• S. aureus, Gram negative bacilli

• < normal flora, quantify and limit ID; no susceptibility• Add comment that organism not predominant on stain

• ID mould, Mycobacteria or Nocardia spp.

Modified from Sharp SE, et. Al. 2003. Cumitech 7B. ASM Press.

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INTERPRETATION OF QUANTITATIVE PSB/BAL

• Dilution Method• Quantify each morphotype present and express as CFU/ml

• Calibrated Loop Method• Quantify each morphotype present and express as log10 colony

count ranges

• Thresholds for significance• PSB > 103 CFU/ml• BAL > 104 CFU/ml

Baselski and Wunderink. 1994. Clin Micro Rev 7:547

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EXAMINE FOR AND ALWAYS REPORT.

• Streptococcus pyogenes

• Group B streptococci in pediatric population

• Francisella tularensis

• Bordetella spp., especially Bordetella bronchiseptica

• Yersinia pestis

• Nocardia spp.

• Bacillus anthracis

• Cryptococcus neoformans

• Molds, not considered saprophytic contaminants

• Neisseria gonorrhoeae

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• Streptococcus pneumoniae

• Haemophilus influenza report beta-lactamase

•

ALWAYS REPORT, BUT DO NOT MAKE AN EFFORT TO FIND LOW NUMBERS, UNLESS THEY ARE SEEN IN THE SMEAR.

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REPORT IF PRESENT IN SIGNIFICANT AMOUNTS, EVEN IF NOT PREDOMINANT

• 1 Moraxella catarrhalis

• 2 Neisseria meningitides

• Report the following for nosocomial infections:

• 3. Pseudomonas aeruginosa

• 4. Stenotrophomonas maltophilia

• 5. Acinotobacter spp.

• 6. Burkholderia spp.

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REPORT IF PRESENT IN SIGNIFICANT AMOUNT AND IF IT IS THE PREDOMINANT ORGANISM IN THE CULTURE,

PARTICULARLY IF SUGGESTS INFECTION WITH MORPHOLOGY CONSISTENT WITH ISOLATE.

• Staphylococcus aureus

• Beta-hemolytic streptococcus B (adults), C, or G

• Single morphotype of gram-negative rod (especially Klebsiella pneumoniae)

• Fastidious gram-negative rods; usually report beta-lactamase

• Corynebacterium spp. if urea positive or from ICU

• Rhodococcus equi in immunocompromised patients

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ATS GUIDELINESDIAGNOSTIC TESTS FOR CAP

• Empiric therapy for outpatients• Macrolide or tetracycline

• Hospitalized patients with CAP

• 2 sets of pre-treatment blood cultures• Pleural fluid Gram stain/culture when appropriate• Studies for Legionella, Mtb, fungi in select patients• Sputum Gram stain/culture only if resistant or unusual pathogen

is suspected• Avoid extensive testing

ATS. 2001. Am J Respir Crit Care Med 163: 1730-1754.

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CRITERIA FOR REJECTING SAMPLES

Mismatch of information on the label and the request

Inappropriate transport temperature

Excessive delay in transportation

Inappropriate transport medium• specimen received in a fixative

• dry specimen

• sample with questionable relevance

Insufficient quantity

Leakage

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• Aerobic Gram stain quantitative bacterial culture

• Fungal stain and culture• Mycobacterial stain and

culture • Viral culture/Respiratory

DFA• Pneumocystis DFA• Legionella culture

IMMUNOCOMPROMISED PATIENTSSUGGESTED BAL PROTOCOL

MANY OTHER CAUSES OF PNEUMONIA WITH ACUTE RESPIRATORY DISEASE & FEVER

Plague Tularemia RICIN toxinStaphylococcal Enterotoxin B

TBLegionella

SARS

S.Pneumoniae

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SUMMARY• Respiratory system can host a variety of microbes

• Normal flora in “restricted areas”

• Susceptibility depends on age, immune system

• Some organisms are adept at evading immune system

• Damage generally due to cytotoxicity and inflammation

• Vaccines are available for some organisms

CHILDHOOD IMMUNIZATIONS CAN REDUCE RESPIRATORY INFECTIONS – FOLLOW THE SCHEDULES

CHILDHOOD IMMUNIZATIONS CAN REDUCE RESPIRATORY INFECTIONS – FOLLOW THE SCHEDULES

Birth 1m 2m 3m 4m 6m 12m 15m 18m 4-6y 11-12y

HBV3

DTP

HBV1HBV2

DTPDTP DTP

HibHib

Hib Hib

Polio Polio Polio

MMR MMR or MMR

Varicella Varicella

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DO REMEMBER

• The culture of lower respiratory specimens may result in more

unnecessary microbiologic effort than any other type of

specimen.”Raymond C Bartlett

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• Programme created by Dr.T.V.Rao MD for Medical and

Health Workers in the Developing World

• Email• doctortvrao@gmail.com