One of the most heavily deployed factoids concerning bed bugs in recent weeks is that substantial numbers of people don’t react to bed bug bites. This has sometimes been expressed as “most people” and it was one of the unfortunate consequences of the publicity surrounding the recent JAMA literature review.
I suppose we must all learn to resist the temptation of making reductive statements about bed bugs, especially as they concern host reactions, an area that is vastly unexamined.
In a short communication to be published in Medical and Veterinary Entomology that should complicate our reading of the JAMA article, University of Sheffield researchers provide an interesting discussion of bed bug bite reactions.
In my opinion these Sheffield bed bug guys are never boring. I quite like them most of the time. They begin with an impatient observation:
Many bedbug ‘fact sheets’ available on the Internet (13 of the first 30 hits in a popular search engine; December 2007) stress that some people are insensitive to bedbug bites and it seems to now be common ‘knowledge’ that a fifth of the population are insensitive to bedbug bites (Ebeling, 1975; Ryckman & Bentley, 1979).
Reinhardt, K., Kempke, D., Naylor, R.A., Siva-Jothy, M.T. (2009) Sensitivity to bites by the bedbug, Cimex lectularius. Medical and Veterinary Entomology. Early view. DOI: 10.1111/j.1365-2915.2008.00793.x
Reinhardt et al. think they know where the idea of an insensitive
25% 20% [my error -RC] comes from, an 80-year old study:
We reviewed all original papers listed in Ryckman & Bentley (1979) and 30 additional case studies and original research articles on human responses to bites. Of those that verified the bedbug Cimex lectularius L. as the causative agent, with at least strong circumstantial evidence, only six studies quantified sensitivity to bedbug bites among a number of people (Table 1). Only three of these six studies reported sensitivity estimates based on people that were at least likely to have been exposed repeatedly to bites. The repeated reporting in the medical and public health literature of 20% insensitivity within the population is apparently based on Kemper’s (1929) study, which showed that eight out of 45 people (17.8%) were insensitive to bedbug bites.
The proportion of subjects reacting to bed bug bites in those 6 studies ranged from 16.7% to 82.2% (the Kemper study). Interestingly, one of these studies was conducted in a camp for displaced persons in Sierra Leone and the sensitivity percentage there was 86%.
In addition to students and researchers, Reinhardt et al. appeared to have persuaded visiting family and friends to volunteer for bed bug bites over a period of three years. Of the 24 people who volunteered for bite tests, 11 of 24 reacted to the first bite, 11 of 12 reacted to the second bite, and 7 of 8 reacted to the third bite. 5 of the 13 who did not react after the first bite did not volunteer for further bite tests. 13 of 24 volunteers did not react the first time, but of those thirteen, 7 reacted after the second bite, and it’s an open question whether the 5 who did not re-volunteer would have reacted after the second bite. Only one of the 24 volunteers did not react after any of the three bite tests.
Latency of response diminished with every bite occurrence, from 7-11 days after the first bite to, for some of the volunteers, 1.5-3 days after the third bite. Four of the volunteers who have continued to feed bed bugs for 6 years show an immediate reaction, within seconds.
The insensitive percentage is hard to pin down, and this is a very small sample, but it’s still very interesting:
In our study, one of 19 individuals who reported the results of their repeated exposure to bites was insensitive (5.3%). However, five people who showed no response to the first experimental bite did not re-volunteer. Any number of these five may also be insensitive, i.e. between one and potentially six out of 24 volunteers (4.2-25%). This range covers the 17.8% published by Kemper (1929) and the 14.0% given in a larger study by Gbakima et al. (2002), which probably involved repeated bites (Table 1). Our result should be verified with a larger-scale study.
The authors make an important point about bed bug bites that we’d do well to keep in mind, namely that reactions to bed bug bites are allergic in nature; the first bite may produce no response. Little can be inferred, therefore, from studies that are not constructed around repeated exposure.
A bed bug infestation, a natural infestation, is all about repeated exposure. This should be studied further, yes? Not like researchers would be hurting for opportunities these days.
In the United States, of course, the most cited insensitive-to-bed-bug-bites statistic’s source is Dr. Jerome Goddard himself.
In the JAMA review article, Goddard and deShazo put it like this:
Detailed accounts of bed bug biting incidents [4-6] demonstrate that not everyone bitten by bed bugs develops a clinical reaction, a finding supported by experimental work with volunteers that reported that only approximately 30% of patients react to bites. 
The problem with this is that the cited study (8) is: Ryckman, R.E. (1985) Dermatological reactions to the bites of four species of Triatominae (Hemiptera: Reduviidae) and Cimex lectularius L. (Hemiptera: Cimicidae). Bulletin of the Society for Vector Ecology, 10,122–125 .
The Ryckman study stopped evaluation of the bite reactions 72 hours after the first (and only) bed bug bite test. As we know, this is not quite enough to judge whether a person will in fact react.
So, the next time you hear or read that most people don’t react to bed bug bites, you might say, hmm…
Kemper is quite beyond me, sorry.