[Bed Bugs] The Sensitivity Spectrum: Human Reactions to Bed Bug Bites

In many respects, bed bugs are the perfect parasite. Under cover of darkness, they feed while their hosts lay sleeping. Their bites are painless so the victim seldom realizes they were bitten until later on. Unlike fleas, ticks or lice, the bed bug scurries away to hidden harborages after feeding to digest its meal. In addition, we all react to bed bug bites differently. Some of us experience characteristic itchy red welts while others show scarcely a mark. In those who do react, symptoms may be delayed days or even weeks, adding to the ambiguity of the encounter.

For those in pest control, it is well known that some customers do not react to bed bug bites, and that this can delay detection and timely intervention. Oft-stated statistics for non-reactivity vary widely — from less than 20 percent to more than 80 percent of the population. Such estimates are based on a handful of studies (some dating back to the 1920s and ’30s) often lacking in details or involving limited numbers of exposed individuals.

To better understand this phenomenon, we conducted the largest survey of its kind involving sensitivity to bed bug bites. The findings presented in this article have important implications for pest managers and the public.

SURVEY PARAMETERS. A multi-question survey was developed to assess people’s sensitivity to bed bug bites. The survey, conducted during spring/summer of 2009, was administered by pest control personnel to customers in Chicago, New York, Cincinnati, Louisville, Atlanta, Los Angeles and Miami. Participation was voluntary and followed institutional guidelines for research ethics. All survey respondents resided in dwellings known to be infested with bed bugs as confirmed by each pest control company. Additional information was obtained on respondent age, gender, ethnicity, type of dwelling and level of infestation (based on a visual inspection of the premises).

A total of 474 individuals participated in the survey. About two-thirds (66 percent) lived in apartments and 15 percent resided in single-family homes. The rest lived in condos/townhomes (9 percent), shelters (7 percent), dormitories (2 percent) or long-term care (less than 1 percent). As noted earlier, each respondent’s home had a confirmed bed bug infestation. In 34 percent of these the infestation level was deemed low (10 or fewer observed bed bugs), 47 percent were considered moderate (11 to 100 bugs), 14 percent had high (101 to 500) numbers of observed bed bugs, while 5 percent had very high numbers (more than 500). Fifty-eight percent of respondents were female and 42 percent were male, and subjects ranged in age from 1 to 90 years old. In terms of ethnicity, 58 percent were Caucasian, 19 percent were African-American, 9 percent were Asian and 7 percent were Hispanic (another 7 percent did not specify).

SENSITIVITY TO BITES. When asked the fundamental question: "Have you experienced any bites or skin reactions from the bed bugs in your dwelling?" 70 percent of respondents said "yes" and 30 percent said "no." Interestingly, level of infestation had no appreciable effect on reactivity — about the same percentage of respondents reported having or not having a reaction whether they were living with low, moderate, high or very high numbers of bed bugs. Numerically more females than males said they were reacting to the bites but the difference was not statistically significant. No significant differences in reactivity were observed relative to ethnicity.

One factor that did seem to affect people’s reactivity to bed bug bites was age. Significantly more people over the age of 65 reported no bites or skin reactions than those who were younger. Forty-two percent of the eldest individuals surveyed said they had no bites or reactions from bed bugs in their dwelling, whereas 26 percent of those aged 11 to 65 reportedly did not react.

High levels of non-reactivity among the elderly were also noted in another bed bug sensitivity survey conducted in Kentucky last year with the Lexington Health Department. In one severely infested apartment building, a whopping 76 percent of elderly tenants (44 of 58) whose units had bed bugs reported no bite reactions. According to Dr. Beth Miller, clinical director of allergy and asthma at the University of Kentucky, immune systems of the elderly are often less responsive to allergens (the medical terminology for this is "anergy"). As a result, elderly patients often do not react as definitively in allergy skin prick tests and the same may be true from insect bites.

Certain medications such as corticosteroids can further suppress the body’s immune response to allergens. Diminished awareness due to other competing health issues may also play a role in why seniors seemingly are less sensitive to bed bug bites. This finding suggests that housing for the elderly should be especially vigilant since these residents may be an even poorer indicator of bed bug presence than the population as a whole. Children aged 1 to 10 in our survey had similar levels of non-reactivity (41 percent) as respondents over the age of 65; however, we felt the sample size for this group (N=17) was too small to make a meaningful statistical comparison.

The welts and itching that often accompany bug bites are the body’s immune response to allergens in insect saliva. There was an interesting relationship in our survey between reported reactions to mosquito bites and reaction to bed bugs — those indicating they were sensitive to mosquito bites also were more sensitive to bed bugs. Individuals who mentioned having a "barely visible" reaction when bitten by mosquitoes had 53 percent reactivity to bed bugs. Respondents who said they typically experience "small (dime-size) welts" from mosquito bites had 77 percent reactivity to bed bugs, whereas those suffering "large (quarter-size)" or "severe (half-dollar size or larger)" swellings from mosquito bites each had 89 percent reactivity to bed bugs.

ADDITIONAL SYMPTOMS. Of those who did experience bites or skin reactions, the majority (72 percent) mentioned having itchy red welts. Half (50 percent) said they experienced redness or discoloration and 28 percent indicated itching in the absence of welts. Twenty-one percent of those having a reaction also mentioned feeling a "pinprick" or "stinging sensation" which may or may not be symptomatic of bed bugs. In terms of bite location, most people reported being bitten on arms (84 percent) or legs (75 percent). Half of those reacting also mentioned being bitten on the chest or back (50 percent), neck (40 percent), hands (40 percent), feet (38 percent) or face (21 percent). Observations by University of Kentucky entomologists suggest that bed bugs have a difficult time biting through most clothing, which presumably is why bites tend to occur where skin is exposed.

Several respondents (N=145, 31 percent) mentioned additional maladies when asked the open-ended question: "Have you had any other symptoms which you attribute to the presence of bed bugs in your home?" Symptoms most often mentioned were "insomnia/sleeplessness (mentioned by 29 percent)," "emotional distress (mentioned by 22 percent)," "anxiety" (by 20 percent) and "stress" (14 percent).

Other oft-mentioned symptoms from respondents living with bed bugs included nervousness, paranoia, anger, frustration, embarrassment, devastation and depression. Anxiety, stress, sleeplessness and depression are medically important symptoms that can lead to other conditions. Dismissing bed bugs as "not a public health pest" on the grounds that they are unproven disease vectors ignores the pain, suffering and emotional distress inflicted on their victims. When government agencies finally concede this point, additional resources may be allocated to combat the problem, as they were years ago.

STUDY IMPLICATIONS. The most telling finding from this study was that many people indeed have little or no reaction from bed bug bites. Although no attempt was made to corroborate self-reporting of sensitivity, the fact that almost one in three respondents (30 percent) living with bed bugs had no perceived reaction has important implications for pest managers and their clients. Bed bug populations can grow discreetly before being discovered. When survey respondents were asked: "About how long have you been aware of the bed bugs in your home?" more than half (51 percent) said one month or less and 76 percent were only aware for one to three months. Even among those living with high or very high numbers of bed bugs, the majority (64 percent) only knew they had them for three months or less.

Previous studies have shown that sensitivity to bed bugs is influenced by prior exposure, as with most allergens. Initial bites often produce no reaction but subsequent ones do. All 474 respondents in our survey were living with infestations and probably were being bitten repeatedly over time. Conversely, people bitten the first time (such as during a one-night hotel stay) might be less likely to react. Prior exposure to bed bugs also influences the latency period between bites and onset of symptoms. With most biting pests, skin reactions usually appear within 24 hours. Noticeable reactions from bed bugs, however, can be delayed a week or longer, especially when there was no previous exposure.

Delayed symptoms often make it difficult to determine if, when, and where bed bugs were encountered; this delay is another reason infestations often go unreported for long periods. Conceivably, a guest accusing a hotel of a problem could have been bitten days earlier at a different establishment. Difficulties tracing bed bugs to their source from delayed reactions can likewise occur in such places as trains, buses, waiting rooms and movie theaters.

As bed bug populations grow, they tend to disperse outward from sleeping areas making extermination more costly and difficult. In multi-occupancy dwellings, such as hotels and apartments, the infestation also can spread to other units before the source unit is discovered. Apart from bite insensitivity or delayed reactions, some do not report a bed bug problem out of embarrassment, or fear of eviction, or having to pay for the extermination. Others simply tolerate living with them. Thus, it is risky to rely solely upon occupants as indicators of infestation.

When it comes to managing bed bugs, vigilance is crucial — a finding learned many years ago by our forefathers. It will be interesting to see if we are willing to make such sacrifices again.

All photos © M. F. Potter

Michael F. Potter and Kenneth F. Haynes are professors at the University of Kentucky. Kevin Connelly (A-Alert Exterminating, Chicago, Ill.), Michael Deutsch (Arrow Exterminating, Lynbrook, N.Y.), Erich Hardebeck (Permakil Pest Control, Covington, Ky.), Don Partin (OPC Pest Control, Louisville, Ky.), and Ron Harrison, Orkin, Atlanta, Ga.) are pest control company owners, managers and technical experts.

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