Nocardia farcinica as a causative agent of lung abscess

Sir,

Nocardia farcinica lung abscess in an immunocompetent adult without any other systemic manifestation of Nocardia is an extremely rare entity. Peculiar pathogens of lung abscess are Staphylococcus aureus, Klebsiella, Pseudomonas aeruginosa and Proteus species. Candida albicans, atypical pathogens like Legionella and Pneumocystis jiroveci may be encountered as well in immunocompromised individuals. Patients with impaired immune mechanisms and cough reflex are most vulnerable for aspiration and abscess formation.

A 45-year-old non-diabetic male, known case of severe persistent bronchial asthma for 10 years (controlled on regular treatment with inhaled beclomethasone 800 µg and formoterol 12 µg per day) presented with high grade continuous fever coupled with cough with phlegm production (not foul smelling) for 10 days and breathlessness for 4 days. Cough had postural variation and was more in right lateral position. On admission temperature was 102^°F and oxygen saturation was 92%. Routine hemogram revealed normal picture except a raised total leukocyte count of 18,000/mm³ with 93% polymorphonuclear neutrophils. Sputum was negative for acid fast bacilli by Ziehl-Neelsen stain and concentration method. Mantoux test revealed induration of 4 mm at 72 hours. Grade 1 clubbing was present. Auscultation revealed decreased entry in left lower lung field with few crackles in upper lung fields of the same side. Chest X-ray revealed a large cavity in left lower lung with irregular margins and air fluid level inside [Figure 1]. Ultrasound-guided aspiration of 100 ml frank pus was done which was examined for culture and sensitivity and the patient was started on empirical injectable antibiotic therapy with amikacin, piperacillin tazobactam and clindamycin. There were no signs of improvement clinically and radiologically even after 1 week of antibiotic therapy and his phlegm production increased in amount and purulency with persistent running fever. Oxygen saturation dropped down to 86% and the patient was now supplemented with oxygen therapy. Meanwhile sputum culture revealed Pseudomonas species sensitive to amikacin and piperacillin tazobactam and subsequent modified Ziehl-Neelsen stain of the Broncho alveolar lavage (BAL) sample revealed typical Nocardia species with delicate beaded branching filaments [Figures 2 and 3]. Sputum was further examined by polymerase chain reaction (PCR) which confirmed the diagnosis of N. farcinica species. Culture on blood agar plates revealed typical chalky white wrinkly colonies of Nocardia after 5 days.”

Figure 1.

Chest X-ray PA view showing a left lower lobe cavitary lesion having a irregular wall and air fluid level inside

Figure 2.

Typical Nocardia species with delicate beaded branching filaments on modified Ziehl-Neelsen stain of BAL fluid

Figure 3.

Slender-shaped Nocardia on modified Ziehl-Neelsen stain of the sputum sample with diluted 1% sulfuric acid

”In vitro” drug sensitivity revealed resistance of Nocardia to amikacin, piperacillin tazobactam, ceftriaxone and sensitive to cotrimoxazole (20 mg/kg) and linezolid (40 mg/kg)

Based on the poor response to antipseudomonal therapy he was put on injectable cotrimoxazole and linezolid therapy. A dramatic response to combination therapy was evident as the phlegm production and fever spikes reduced substantially within 5 days of injectable therapy. Total leukocyte counts settled down to 8000/mm³ with normal polymorphonuclear neutrophils. Radiological improvement was evident and oxygen saturation was now above 96%. The patient was discharged on oral cotrimoxazole therapy for 1 month to ensure a complete cure of the disease and linezolid was stopped after 7 days. Subsequent cultures on follow up were negative. Complete radiological clearance was seen in 8 weeks. Oral trimethoprim sulfamethoxazole (TMP-SMX) was continued for 6 months to avoid relapse of the disease.

N. farcinica mainly affects immunocompromised patients, however local immunosuppression in this patient due to regular intake of inhaled corticosteroids cannot be ruled out and is a matter of debate. Pulmonary manifestation of Nocardia ranges from pneumonia, suppurative lung disease to empyema. Alcoholism, chronic lung disease and HIV infection are three important risk factors for pulmonary Nocardiosis. The biggest challenge with N. farcinica infection is the difficulty to arrive at its definitive diagnosis due to scarcity of infection with this pathogen in immunocompetent hosts, as a result it is mostly overlooked or misdiagnosed as other pathology.[1] Infection with N. farcinica should always be suspected when there is a preceding history of contaminated water or soil ingestion and the patient is not responding to standard anti microbial therapy. After looking at the anatomical location of lung abscess in this case, aspiration can be a possibility as the patient had artificial dentures. Identification of N. farcinica is important because of its aggressive nature, tendency to disseminate and resistance to antibiotics.[2,3] Kinyoun acid fast stain (for cultured organisms) is the main stay of diagnosis for Nocardia where they appear as red-stained filaments against a blue background. PCR to identify the Nocardia species is usually the gold standard for diagnosis. They grow readily over simple culture media such as blood agar and Lowenstein Jensen agar. Therapy with oral TMP-SMX remains the main stay of treatment for N. farcinica but due to emergence of resistant strains to amikacin and cotrimoxazole parenteral imipenem and linezolid is the drug of choice for inpatients requiring parenteral antibiotic therapy. The mortality due to N. farcinica infection is about 14% to 40% that increases significantly with dissemination to CNS (central nervous system).[4,5] Jonathan et al.[6] observed a death rate of 39% associated with N. farcinica despite aggressive therapy with TMP-SMX.

We strongly emphasize on determining the species of Nocardia and its drug-sensitivity pattern to improve the outcome from the dreaded disease which can be fatal otherwise. Any lung abscess in a previously healthy patient not responding to usual empirical antibiotic and antifungal therapy should be looked upon with high index of suspicion for Nocardiosis and if Nocardia is isolated in laboratory, special emphasis should be laid upon determining the species and its drug susceptibility pattern after culture.