Moraxella catarrhalis


-Moraxella catarrhalis are gram-negative cocci that pair as kidney-shaped diplococci and thus morphologically similar to Neisseria 

-In contrast to pathogenic Neisseria, Moraxella lacks antiphagocytic capsules and IgA proteases.

-It is found only in humans and is transmitted by respiratory aerosol.

Symptoms & Signs

-It causes otitis media and sinusitis primarily in children

-it causes bronchitis and pneumonia, primarily in older people with chronic obstructive pulmonary disease


-in culture, it grows as round, opaque colonies on blood and chocolate agar, which typically turn pink after 48 hours

-A characteristic feature of M. catarrhalis: its colonies slide across agar without disruption (hockey puck sign) 


-Antibiotics: amoxicillin-clavulanate, ampicillin-sulbactam, trimethoprim-sulfamethoxazole, macrolides (azithromycin, clarithromycin) fluoroquinolones (ciprofloxacin), and cephalosporins

-M.catarrhalis produces a β-lactamase and is resistant to ampicillin.

Haemophilus influenza

Haemophilus influenzae are pleomorphic, oxidase positive, gram-negative coccobacilli rods that commonly colonize and infect the human respiratory tract. 

-H. influenzae are found on the mucous membranes of the upper respiratory tract in humans with the nasopharynx as the most common site of long-term colonization 

-Clinically, H. influenzae is similar to S. pneumoniae, with a slower onset.

-it is spread by airborne droplets or by direct contact with secretions or fomites. 

-its most serious manifestation is meningitis 

-the most prominent strain is Type b 

-risk factors include alcoholism, smoking, chronic lung disease, advanced age, and HIV infection 

Symptoms & Signs 

H influenzae may cause sinusitis, otitis, bronchitis, epiglottitis, pneumonia,pericarditis, cellulitis, arthritis, meningitis, and endocarditis. 


Diagnosis can be established by showing gram-negative coccobacilli in culture


Antibiotics: Beta-lactams (amoxicillin, amoxicillin-clavulanate), cephalosporins, fluoroquinolones, macrolides, and tetracyclines

-In Hib meningitis, administration of glucocorticoids reduces the incidence of neurologic sequelae 


All children should be immunized with an Hib conjugate vaccine with the primary series at 2–6 months of age, and a booster dose at 12–15 months of age.


Diphtheria is an acute toxin-mediated infection of the upper respiratory tract or skin caused by toxin-producing Corynebacterium diphtheriae

-Corynebacteria are gram-positive, non-spore forming, club-shaped rods with a beaded appearance on Gram stain

-it has largely been eradicated in developed nations through widespread vaccination

-It is transmitted from person to person through respiratory secretions or skin lesions. 

Symptoms & signs

Respiratory diphtheria: fever, sore throat with a gray pseudomembrane, malaise, dysphagia, barking cough, stridor, hoarseness, swollen cervical lymph nodes, brawny edema of the neck (bull neck), tachycardia out of proportion to fever

Cutaneous diphtheria: Ulcerative lesions  

Diphtheritic myocarditis:  rapid, thready pulse, arrhythmias, circulatory collapse

Diphtheritic neuropathy: Paralysis of the muscles of the soft palate and pharynx, Peripheral neuritis


-Diagnosis is clinical

-Diagnosis is confirmed by isolation of bacteria by culture of a nasopharyngeal swab

-Culture shows club-shaped gram-positive rods in clusters of parallel rays (palisades), in V or L shaped formations referred to as “Chinese characters.” 

-Laboratory must be notified of suspicion in advance


The treatment of choice is antitoxin

To be effective, diphtheria antitoxin should be administered within 48 hours 

Treatment includes antitoxin, antibiotics (Procaine penicillin, erythromycin) , and respiratory support as needed


Influenza is an acute respiratory illness caused by influenza A or B viruses

-Transmission occurs primarily by droplet nuclei

-The incubation period is 1–4 days

-The average duration of influenza virus shedding in immunocompetent patients: 5 days 

Symptoms & Signs

-Sudden onset of fever, rhinorrhea, chills, pharyngitis, hoarseness, nonproductive cough,malaise, myalgias, enlargement of cervical lymph nodes, tracheal tenderness 

-The major complication of influenza is pneumonia (most common is  Pneumococcal pneumonia, most serious is staphylococcal pneumonia


The best specimens for diagnostic testing: nasopharyngeal swabs and nasal aspirate or lavage fluid 

RT-PCR, rapid molecular assays, antigen detection assays, viral culture 


Treatment is supportive

Antiviral therapy: Oseltamivir, inhaled zanamivir (it can cause bronchospasm),peramivir, baloxavir 


Annual administration of influenza vaccine is the most effective measure for preventing influenza and its complications. 

Ebola virus disease

-Ebola virus is a single-stranded, nonsegmented, negative-polarity RNA virus

-It causes Ebola hemorrhagic fever (EHF)

-the virions have ‘shepherd’s crook’ appearance 

Symptoms & Signs 

-Transmission from human to human occurs via blood and body fluids

-Fever, headache, sore throat, myalgia, arthralgia, vomiting, diarrhea, rash, uveitis, shock, multiorgan failure 


-Virus is detected with a real-time RT-PCR, ELISA, and IgM antibody serum tests 


-There are no approved antiviral medications for treatment of Ebola virus disease

-Supportive therapy with intravenous fluids and electrolytes 

Q. What are the most common complications of EVD? Hypovolemic shock and multiorgan failure