An outbreak of Legionella longbeachae infection in an intensive care unit?

During a nine-day period, five patients in a 14-bed intensive care unit (ICU) were shown to have seroconverted with a four-fold or greater rise in serum antibody titre to Legionella longbeachae serogroup 1. A further two patients were observed to have high titres consistent with previous exposure but earlier serum samples were not available for comparison. No patients had antibody responses to Legionella pneumophila serogroups 1 and 2. L. longbeachae was not cultured from respiratory secretions from patients or from the environment within the unit. Legionella anisa was recovered from one cooling tower on the ninth floor of the tower block. The ICU is located on the first floor of the same tower and receives external air from two vents, one on the eastern and the other on the western aspect. All patients with serological evidence of L. longbeachae infection were concomitantly infected with multiresistant Staphylococcus aureus, and were located in bays on the eastern side of the unit. A large pigeon nest was discovered within 1-2 m of the eastern vent. Following removal of the birds' nest, no further cases were seen on routine screening of all patients within the unit over the next eight weeks. Alternatively, seroconversion may have been related to demolition of the adjacent nine-storey nurses home. This was begun one month before the first case was diagnosed and was completed four months later. The periodic northerly winds could have carried legionellae from the demolition site directly over the block housing the ICU and may have concentrated them near the eastern air vent. All patients had pneumonia, which was probably multifactorial in origin. There is some uncertainty whether the serological responses seen were an epiphenomenon or were truly indicative of infection with L. longbeachae.

Evaluation of a commercial enzyme-linked immunosorbent assay for detection of immunoglobulin M antibody in diagnosis of human leptospiral infection.

The PanBio Leptospira immunoglobulin M (IgM) enzyme-linked immunosorbent assay (ELISA) is a commercially available screening test for the diagnosis of acute leptospiral infection. The ability of the test to diagnose early or recent Leptospira interrogans infection was assessed by testing sera with known microagglutination test (MAT) titers to serovars pomona, hardjo, copenhageni, and australis. The IgM ELISA detected all 41 cases of early or recent leptospiral infection (sensitivity, 100%), with a positive ELISA result seen in many cases before MAT antibody titers reached 1:50. Thirty-eight of 41 patients showed seroconversion (fourfold or greater increase in titer by MAT, 2 of 41 patients had a single sample with elevated titer, and 1 patient from whom leptospires were isolated from a blood sample failed to show MAT titers, despite a seroconversion (negative to positive result) in the ELISA. Follow-up sera obtained from 8 of 12 patients (67%) for 3 to 48 months after the acute stage of illness showed persisting IgM antibody. However, the range of levels detected in these samples (maximum ELISA ratio, 2.0) was lower than the range seen when infection was recent. Reactivity in the IgM ELISA was observed for only 1 of 59 serum samples from asymptomatic donors (specificity, 98%) and 16 of 233 serum samples from patients with Ross River virus, brucella, Epstein-Barr virus, cytomegalovirus, mycoplasma, Q-fever, toxoplasma, hepatitis A virus, Treponema pallidum, or Borrelia burgdorferi infection (specificity, 93%), with the majority of these patients showing lower levels of IgM in comparison to those in patients with leptospiral infection. We conclude that this ELISA is sufficiently sensitive for use as an initial screen for leptospiral infections, with subsequent confirmation of positive test results by MAT.