Epidemiologic Investigation of Immune-Mediated Polyradiculoneuropathy among Abattoir Workers Exposed to Porcine Brain

Abstract

BackgroundIn October 2007, a cluster of patients experiencing a novel polyradiculoneuropathy was identified at a pork abattoir (Plant A). Patients worked in the primary carcass processing area (warm room); the majority processed severed heads (head-table). An investigation was initiated to determine risk factors for illness.Methods and ResultsSymptoms of the reported patients were unlike previously described occupational associated illnesses. A case-control study was conducted at Plant A. A case was defined as evidence of symptoms of peripheral neuropathy and compatible electrodiagnostic testing in a pork abattoir worker. Two control groups were used - randomly selected non-ill warm-room workers (n = 49), and all non-ill head-table workers (n = 56). Consenting cases and controls were interviewed and blood and throat swabs were collected. The 26 largest U.S. pork abattoirs were surveyed to identify additional cases. Fifteen cases were identified at Plant A; illness onsets occurred during May 2004–November 2007. Median age was 32 years (range, 21–55 years). Cases were more likely than warm-room controls to have ever worked at the head-table (adjusted odds ratio [AOR], 6.6; 95% confidence interval [CI], 1.6–26.7), removed brains or removed muscle from the backs of heads (AOR, 10.3; 95% CI, 1.5–68.5), and worked within 0–10 feet of the brain removal operation (AOR, 9.9; 95% CI, 1.2–80.0). Associations remained when comparing head-table cases and head-table controls. Workers removed brains by using compressed air that liquefied brain and generated aerosolized droplets, exposing themselves and nearby workers. Eight additional cases were identified in the only two other abattoirs using this technique. The three abattoirs that used this technique have stopped brain removal, and no new cases have been reported after 24 months of follow up. Cases compared to controls had higher median interferon-gamma (IFNγ) levels (21.7 pg/ml; vs 14.8 pg/ml, P<0.001).DiscussionThis novel polyradiculoneuropathy was associated with removing porcine brains with compressed air. An autoimmune mechanism is supported by higher levels of IFNγ in cases than in controls consistent with other immune mediated illnesses occurring in association with neural tissue exposure. Abattoirs should not use compressed air to remove brains and should avoid procedures that aerosolize CNS tissue. This outbreak highlights the potential for respiratory or mucosal exposure to cause an immune-mediated illness in an occupational setting.

What Differentiates Symptomatic from Asymptomatic Women with Lichen Sclerosus?

“…Exposure to porcine antigens has been proven to induce autoimmune disease, namely a polyradiculoneuropathy in patients who worked in a pork abattoir, processing severed heads [4]. Although in this case the particles were inhaled, it can represent a possible mechanism for inciting an autoimmune response.…”

Chronic Inflammatory Demyelinating Polyneuropathy

“…Earlier reported prevalence has ranged from 1 to 7.7 per 100,000, and increased with advancing age with a peak incidence at 40–60 years of age [5–7]. In Olmstead County, the incidence of CIDP was more recently estimated to be 1.6/100,000/year with a prevalence of 8.9/100,000 [5].…”

Multifocal Motor Neuropathy, Multifocal Acquired Demyelinating Sensory and Motor Neuropathy, and Other Chronic Acquired Demyelinating Polyneuropathy Variants

“…50 In addition, we and others described prolonged distal latencies, temporal dispersion, slow conduction velocity, and delayed or absent F-waves on motor NCS in MMN. 22, 25, 29, 51, 52 Conduction block is not essential to the diagnosis of MMN if other features of demyelination are detected. 22, 25 In our series of MMN patients, 22 only 31% had conduction block; 44% had temporal dispersion, and 94% had other electrodiagnostic features of demyelination with superimposed axonal degeneration (Table 2).…”