Pulmonary infection due to Nocardia exalbida complicated with pneumococcal pneumonia

Case presentation: A 68-year-old man was hospitalized because of pneumococcal pneumonia. Although his symptoms improved immediately after administration of antipneumococcal antibiotics, patchy opacity on the chest X-ray remained and pyrexia recurred. Administration of trimethoprim/sulfamethoxazole, given after seropositivity against human immunodeficiency virus type 1 was confirmed and Nocardia-like organisms were detected from the sputa, completely resolved his symptoms. The recovered organism was identified as N. exalbida by comparison of 16S rRNA gene sequences.


Introduction
Members of the genus Nocardia, a group of aerobic actinomycetes forming Gram-positive branching filaments, are widely found in the environment, including in soil and water.They occasionally cause human diseases, especially among immunocompromised hosts, through direct inoculation of the skin or inhalation into the lung (Wilson, 2012).To date, more than 30 Nocardia spp.have been described as human pathogens.Taxonomy in the genus through biochemical characterization has been complicated because of technical difficulties.In contrast, recent advance in molecular methodologies, including analyses of 16S rRNA gene sequences, facilitates precise identification of the species (Brown-Elliott et al., 2006).
Nocardia exalbida is a new Nocardia sp.first recovered from materials of immunocompromised humans and characterized by Iida et al. (2006).Since then, only a few cases of N. exalbida infection have been described in the literature (Mizota et al., 2007;Ono et al., 2008;Imai et al., 2011;Milman et al., 2011).Here, we report a case of pulmonary infection caused by N. exalbida in a human immunodeficiency virus type 1 (HIV-1)-infected patient, which became evident after treatment of antecedent pneumococcal pneumonia.

Case report
A 68-year-old Japanese man was admitted to a local hospital because of fever and impaired consciousness.A chest Xray revealed infiltration of both sides of the lower lung fields (Fig. 1a).Administration of cefozopran and clindamycin promptly improved the manifestations.The antibiotics were switched to cefotiam alone and given for a total of 2 weeks because Streptococcus pneumoniae susceptible to the drug was recovered from the blood drawn on the admission.Two weeks after the completion of the anti-pneumococcal treatment, the patient became febrile again.Bronchoscopy was performed on day 28 of admission because patchy opacity remained on segment 9 of the right lobe (Fig. 1b).Bacterial and histopathological examinations of bronchoalveolar lavage fluid Abbreviations: HIV-1, Human immunodeficiency virus type 1; TMP/ SMX, trimethoprim/sulfamethoxazole.demonstrated no significant micro-organism but many cells containing intranuclear inclusions, indicating activation of cytomegalovirus.Following a work-up of immunosuppression, HIV-1 infection with a CD4-positive lymphocyte count of 20 ml 21 and a plasma viral load of 1.2| 10 5 copies ml 21 was confirmed.Intravenous cefotiam was repeatedly administered immediately after the bronchoscopy until the patient was transferred to our hospital on day 41.No anti-cytomegalovirus agent was given because the patient's respiratory conditions did not deteriorate under the treatment with cefotiam.
At the transfer, the patient was afebrile but slightly disoriented with a blood pressure of 96/60 mmHg and arterial oxygen saturation in room air of 98 %.Laboratory findings included hypochromic anaemia (erythrocytes: 2.45| 10 6 ml 21 ; haemoglobin: 7.1 g dl 21 ), elevation of the Creactive?level (3.98 mg dl 21 ) and positive results for rapid plasma reagin (46.8 RPR units) and Treponema pallidum latex agglutination.Computed tomography revealed no remarkable findings on the brain.A lumber puncture indicated no increased intracranial pressure or the presence of pleocytosis, Cryptococcus antigens and syphilitic reactions in the cerebrospinal fluid.From day 4 of the transfer, intermittent fever up to 39 uC reappeared.Although oral amoxicillin-clavulanate was given because aspiration pneumonia was suspected and serum syphilitic reactions were positive, his productive cough worsened.The fever gradually subsided after one single-strength tablet of trimethoprim/sulfamethoxazole (TMP/SMX) day 21 was given for prophylaxis of pneumocystosis on day 14.The daily dose of TMP/SMX was increased to six tablets (approx.12 mg (kg body weight) 21 for the TMP component) on day 21 because Gram-positive, acid-fast (with the modified Kinyoun method) branching filamentous bacteria, suggesting Nocardia spp., were detected from the sputum but was reduced to three tablets on day 27 because severe appetite loss emerged.Thereafter, his productive cough and intermittent fever disappeared and the size of the patchy opacity on the chest X-ray diminished (Fig. 1c).The patient was transferred to a long-term care facility on day 84, at which point the plasma HIV-1 load decreased to an undetectable level under antiretroviral therapy with zidovudine, lamivudine and raltegravir.The same dose of TMP/SMX was administered for a total of 12 months, followed by a prophylactic dose against pneumocystosis (one single-strength tablet day 21 ).On a follow-up one and a half years after the discharge from our hospital, the patient showed no recurrence of nocardiosis, although the TMP/SMX prophylaxis was still given.
The organism suspected of being Nocardia sp., recovered from the sputum on day 21, was further examined.The 16S rRNA gene of the organism was amplified by PCR (Lane, 1991) and a 1392 nt product was sequenced with the ABI PRISM 3130 Genetic Analyzer (Applied Biosystems Japan).An analysis with BLAST showed that the sequence was 100 % nucleotide identity to that of N. exalbida IFM 0803?(GenBank accession no.AB187522).MICs against the organism, measured with the broth microdilution method described by the Clinical and Laboratory Standards Institute (CLSI, 2011) using a DryPlate (Eiken Chemical), were as follows: TMP/SMX, 0.25/4.75mg ml 21 ; imipenem, v0.5 mg ml 21 ; cefotiam, 4 mg ml 21 cefepime, 2 mg ml 21 ; cefozopran, 2 mg ml 21 ; ciprofloxacin, 2 mg ml 21 .

Discussion
In the present case, the patient's illness was first diagnosed as pneumococcal pneumonia because of typical findings on the chest X-ray and recovery of S. pneumoniae from the blood.However, administration of anti-pneumococcal antibiotics incompletely ameliorated the patient's symptoms.The residual manifestations resolved after administration of TMP/SMX, following detection of Nocardia-like organisms in the sputum.The recovered organism was identified as N. exalbida by molecular analysis.These results showed that the patient in the present case contracted pulmonary infection due to both S. pneumoniae and N. exalbida, the latter of which became evident afterwards.
To date, six other cases of N. exalbida recovery from human materials have been described in the English literature (Table 1): two from patients with pulmonary infection (Iida et al., 2006;Imai et al., 2011), one each with endogenous endophthalmitis (Milman et al., 2011), keratitis (Mizota et al., 2007) and brain abscess (Ono et al., 2008), and one with an undescribed location (Iida et al., 2006).Interestingly, five of the six cases were reported from Japan, suggesting that N. exalbida is more prevalent in this country than in other areas (Ono et al., 2008).Detailed clinical courses have been described in four cases, in which three patients were favourably managed with antimicrobial therapies only, but the other, suffering from endophthalmitis, received enucleation followed by antibacterial treatment (Milman et al., 2011).In vitro studies demonstrated that all examined N. exalbida strains, including the one in the present case, were susceptible to TMP/SMX, the drug most commonly used for treatment of nocardiosis (Wilson, 2012).In addition, several other antibiotics, including cefotaxime, imipenem, minocycline and amikacin, showed good activity against the examined strains, indicating that these agents may be used in place of TMP/SMX for treatment of N. exalbida infection.Indeed, pulmonary N. exalbida infection occurring in an HIV-1-infected patient having hypersensitivity to TMP/SMX was successfully treated with intravenous imipenem plus amikacin and subsequent oral garenoxacin (Imai et al., 2011).
Because of the indolent onset and chronic progression, pulmonary nocardiosis has occasionally been complicated with other pulmonary infections, including pneumocystosis, tuberculosis, aspergillosis and cytomegalovirus infection.In contrast, co-infection with pathogens causing acute pneumonia in communities has rarely been reported (Brown et al., 1986;Wilson et al., 1989;Javaly et al., 1992;Peleg et al., 2007;Ambrosioni et al., 2010).In the present case, anti-pneumococcal treatments eliminated most manifestations of pneumonia on the chest X-ray but disclosed patchy opacity in the right lower lung lobe, which diminished after TMP/SMX was given.Thus, we consider that the residual lesion was caused by nocardial infection, which was obscured during the treatment of pneumococcal pneumonia.The present case illustrates that underlying nocardiosis should be considered when pulmonary symptoms of patients with acute bacterial pneumonia are recurrent, despite administration of appropriate treatments.
In the present case, it was approximately 2 months after the initial presentation that diagnosis of nocardiosis was made.
One reason for the delay in diagnosis was the fact that Nocardia-like organisms were not detected in the bronchoalveolar lavage fluid examined in the referring hospital.We consider that the negative result may have been due to antecedent administration of anti-pneumococcal agents, especially cefozopran and cefotiam.According to the breakpoints for pulmonary infection published by the Japanese Association of Chemotherapy (Saito, 1995;Saito et al., 1999), the MICs for cefozopran and cefotiam against the recovered N. exalbida strain were in the range of susceptibility.However, the drugs were only given for a total of 2 weeks, a duration long enough to treat pneumococcal pneumonia but insufficient to prevent relapse of pulmonary nocardiosis (Wallace et al., 1982;Uttamchandani et al., 1994).Susceptibility of nocardiae to antibiotics other than TMP/STX varies in their species (Wilson 2012).Thus, physicians should be aware of the possibility that preceding uses of certain antibiotics unexpectedly interfere with diagnosis of nocardiosis.
In conclusion, we have described a case of N. exalbida infection, which was complicated with pneumococcal pneumo-

Fig. 1 .
Fig. 1.Chest X-rays taken on admission to the referring hospital (a), 1 day before performing bronchoscopy (b), and 50 days after administration of TMP/SMX started (c).Infiltration initially existing on both sides of the lower lung field [indicated with arrows in (a)] and improved after administration of antibiotics, but patchy opacity remained in the right lower lobe [arrowhead in (b)], which almost disappeared after treatment with TMP/SMX (c).