In 2000 the CDC published a review of its own Cleveland investigation into infant lung bleeding and Stachybotrys chartarum. Three analysis choices had inflated the headline result. The conclusion: the association was “not proven.”
Almost every conversation about mold in a house arrives carrying one word: toxic. That word has a specific origin, and it is worth knowing where it came from — because the agency that produced the number behind it went back, checked the work, and reported that the number did not hold.
What happened in Cleveland
Between January 1993 and December 1994, ten infants in the Cleveland area were identified with acute idiopathic pulmonary hemorrhage: sudden bleeding into the lungs. They lived in seven contiguous postal tracts. One died. The clinical picture was unusual — the acute presentation in all ten cases, a narrow age distribution from six weeks to six months, and no iron deficiency.
CDC described the cluster in MMWR in December 1994 and again in January 1997. A case-control study reported that the hemorrhage was associated with two things: major household water damage in the six months before illness, and increased levels of measurable household fungi, including the toxin-producing mold Stachybotrys chartarum, commonly called by its synonym Stachybotrys atra. Some isolates recovered from study homes were shown in the laboratory to produce trichothecene mycotoxins.
The published estimate: an odds ratio of 9.8 for a change of 10 colony-forming units per cubic meter of airborne S. chartarum.
The hypothesis was that infant pulmonary hemorrhage might be caused by exposure to potent mycotoxins produced by S. chartarum or other fungi growing in moist household environments.
That finding traveled. As CDC itself later recorded, it was cited in environmental health guidelines, in congressional testimony and in the popular media, and it influenced the closure of public buildings, cleanup and remediation decisions, and litigation. Despite the original paper’s own caution that “further research is needed to determine…causal[ity],” the 9.8 became the number behind the phrase “toxic black mold” as most people use it today.
Then CDC reviewed its own investigation
In June 1997 a CDC scientific task force, reviewing the agency’s handling of the problem, advised the CDC director that concerns about the role of S. chartarum in pulmonary hemorrhage needed to be addressed. CDC convened a multidisciplinary internal working group of senior scientists and separately sought the individual opinions of outside experts. The two groups reviewed the Cleveland investigation independently. Their findings were published in MMWR on 10 March 2000.
The working group found the reported odds ratio of 9.8 to be, in its words, “statistically unstable and potentially inflated.” Three influential steps in the analysis were identified.
9.8 → 5.5 → 1.9, and separately 9.8 → 1.5.
One. The mean airborne S. chartarum concentrations for each household had been calculated incorrectly. Substituting the corrected means reduced the odds ratio by 44%, to 5.5.
Two. The mean value for one case home had been imputed at 4 CFU/m3. That sample had been collected many months after the others and, along with everything else collected at the same time, produced unusually heavy growth of non-Stachybotrys fungi. Excluding that household and correcting the means reduced the odds ratio to 1.9.
Three. Cases and controls had been matched on age. Subject age would not be expected to influence a concurrent measurement of airborne fungi, and did not correlate with the mean S. chartarum count. Analysis without the matching variable reduced the odds ratio from 9.8 to 1.5.
Two more problems sat alongside the arithmetic. Sampling was supposed to be blinded, but one investigator correctly inferred the identity of many case homes and, wanting to be certain of finding culturable fungi where they were present, collected twice as many air samples from case homes as from control homes. Investigators also used aggressive, non-standardized methods to generate artificial aerosols for sampling — vacuuming carpets, pounding on furnace ducts and furniture — which raises the potential for differential exposure assessment if sampling was not truly blind.
And when the reviewers looked only at homes classified as water damaged, culturable airborne S. chartarum was present in four of eight case homes and three of seven control homes. The reviewers called these similar percentages and said they provided little evidence of a difference. The numbers are small. But as the reviewers put it, if the water-damage classifications were correct, this would suggest that water damage, or an unrecognized correlate of water damage, may be confounding any perceived association with S. chartarum itself.
The reviewers noted the pattern did not repeat elsewhere. Acute infant pulmonary hemorrhage is not consistent with historic accounts of animal and human illness caused by S. chartarum or related toxigenic fungi. Clusters have not been reported in other flood-prone areas where these fungi would be favored. And the mold-disease association observed in Cleveland was not observed in the investigation of a similar cluster in Chicago.
What CDC actually concluded
CDC’s stated conclusion was that “serious shortcomings in the collection, analysis, and reporting of data resulted in inflated measures of association and restricted interpretation of the reports,” that the associations “should be considered not proven,” and that “the etiology of AIPH is unresolved.”
This is the part that gets misread in both directions. It is not a finding that mold is harmless. CDC committed in the same report to continuing to investigate cases of acute infant pulmonary hemorrhage, to continuing to consider household water damage and exposure to environmental hydrophilic fungi such as S. chartarum among possible causes, to developing a standard surveillance case definition, and to improving its own sampling and laboratory methods. What the review removed was a specific number, not a hypothesis.
What does have numbers behind it
Repairing wet buildings does. The Cochrane review of remediation (Sauni and colleagues, published February 2015) searched eight databases and pooled 12 studies with 8,028 participants: two randomized controlled trials with 294 participants, one cluster-randomized trial with 4,407, and nine controlled before-after studies with 3,327. The interventions ranged from thorough renovation to cleaning only.
Repairing houses: wheezing OR 0.64 (95% CI 0.55–0.75); rhinitis OR 0.57 (0.49–0.66).
Repairing mold-damaged houses decreased asthma-related symptoms in adults, including wheezing, and respiratory infections, including rhinitis — two studies, moderate-quality evidence. Repairing a mold-damaged office building also reduced asthma-related and other respiratory symptoms, though on very low-quality evidence.
The same review carries an honest null. For children, the authors found no difference between repaired houses and receiving information only, measured as the number of asthma days or emergency department visits for asthma — one study, moderate-quality evidence. And in schools, out of many symptom measures, only pupils’ visits to physicians for a common cold were less frequent after remediation; for other respiratory symptoms the results were inconsistent, and for adult staff there was no clear evidence of benefit. The authors’ own summary of the quality: very low to moderate.
What gets lost in the black mold marketing
An industry prices off a species name. A lab report comes back with Stachybotrys on it and the quote changes, sometimes by a multiple. But the colony count that carried the famous 9.8 collapsed under three routine analysis corrections, and there is no health-based guideline anywhere that sets a safe airborne spore count for any genus — which means any spore number offered to you as a threshold was set by whoever is selling the service.
The equipment sold against mold has the same problem. HEPA filtration captures particles that reach the filter, including spores already airborne, but it does nothing about the water producing them, and musty odor is a mixture of volatile gases that particle filtration does not remove. The EPA is direct that ozone generators are lung irritants rather than effective air cleaners and should not be operated in occupied spaces. Fungicide applied to a wall that is still wet buys a few weeks.
What the data supports
Find the water first. Roof and window leaks, plumbing, condensation on cold surfaces in winter, and ground moisture rising through crawlspaces and slab edges. In the Portland–Vancouver climate the last of those is the quiet default rather than the exception, and it often produces no dramatic stain to find.
Treat a species name as information, not a verdict. Knowing what is growing tells you something about how long it has been wet and what conditions it likes. It does not by itself tell you how sick anyone will be, and it should not by itself set a price.
Ask what moisture was measured. Relative humidity, surface moisture readings, dew point at cold surfaces — the conditions that produce growth are measurable and repeatable in a way that a single air sample on a single day is not.
Ask which guideline a threshold comes from. If anyone quotes a spore count as a health threshold, that is a fair and specific question, and it has a short answer.
Fix the building, and expect the benefit to be modest and uneven. Cochrane compared repair against doing nothing, against giving the family information, and full repair against partial. Where a benefit showed up it was in adults in repaired houses. In children and in schools it largely did not. That is a real finding, and it is still a stronger basis for action than any spore count.
None of this is medical advice. The Cleveland cluster was and remains a real cluster of a serious illness in ten infants, one of whom died, and CDC’s 2000 review did not resolve what caused it. What the review established is narrower and still important: the specific odds ratio linking that illness to Stachybotrys chartarum did not survive reanalysis, and a great deal of commercial and legal activity has been built on an association its own authors’ agency describes as not proven, resting on a figure that agency calls statistically unstable and potentially inflated.
Want to know what is in your own air, rather than what a species name is worth?
illumenair tests indoor air quality and mold in Portland and Vancouver homes, room by room. We measure and report — we do not remediate, so the result is not a sales pitch for the repair.
971-363-5626 · info@illumenair.com · www.illumenair.com
Sources: CDC. Update: Pulmonary Hemorrhage/Hemosiderosis Among Infants — Cleveland, Ohio, 1993-1996. MMWR Morb Mortal Wkly Rep, 2000;49(9):180-4. — Sauni R, Verbeek JH, Uitti J, Jauhiainen M, Kreiss K, Sigsgaard T. Remediating buildings damaged by dampness and mould for preventing or reducing respiratory tract symptoms, infections and asthma. Cochrane Database of Systematic Reviews, 2015, Issue 2, Art. No.: CD007897, doi:10.1002/14651858.CD007897.pub3.